


Internet Engineering Task Force                             J. Livingood
Internet-Draft                                                   N. Mody
Intended status: Informational                              M. O'Reirdan
Expires: July 12, 2012                                           Comcast
                                                         January 9, 2012


      Recommendations for the Remediation of Bots in ISP Networks
                 draft-oreirdan-mody-bot-remediation-20

Abstract

   This document contains recommendations on how Internet Service
   Providers can manage the effects of computers used by their
   subscribers, which have been infected with malicious bots, via
   various remediation techniques.  Internet users with infected
   computers are exposed to risks such as loss of personal data, as well
   as increased susceptibility to online fraud.  Such computers can also
   become an inadvertent participant in or component of an online crime
   network, spam network, and/or phishing network, as well as be used as
   a part of a distributed denial of service attack.  Mitigating the
   effects of and remediating the installations of malicious bots will
   make it more difficult for botnets to operate and could reduce the
   level of online crime on the Internet in general and/or on a
   particular Internet Service Provider's network.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 12, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Key Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction and Problem Statement . . . . . . . . . . . . . .  5
   3.  Important Notice of Limitations and Scope  . . . . . . . . . .  7
   4.  Detection of Bots  . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Notification to Internet Users . . . . . . . . . . . . . . . . 12
   6.  Remediation of Hosts Infected with a Bot . . . . . . . . . . . 18
     6.1.  Guided Remediation Process . . . . . . . . . . . . . . . . 20
     6.2.  Professionally-Assisted Remediation Process  . . . . . . . 22
   7.  Failure or Refusal to Remediate  . . . . . . . . . . . . . . . 22
   8.  Sharing of Data from the User to the ISP . . . . . . . . . . . 22
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   10. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 23
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
   13. Informative references . . . . . . . . . . . . . . . . . . . . 25
   Appendix A.  Examples of Third Party Malware Lists . . . . . . . . 27
   Appendix B.  Document Change Log . . . . . . . . . . . . . . . . . 27
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32



















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1.  Key Terminology

   This section defines the key terms used in this document.

1.1.  Malicious Bots, or Bots

   A malicious or potentially malicious "bot" (derived from the word
   "robot", hereafter simply referred to as a "bot") refers to a program
   that is installed on a system in order to enable that system to
   automatically (or semi-automatically) perform a task or set of tasks
   typically under the command and control of a remote administrator, or
   "bot master".  Bots are also known as "zombies".  Such bots may have
   been installed surreptitiously, without the user's full understanding
   of what the bot will do once installed, unknowingly as part of
   another software installation, under false pretenses, and/or in a
   variety of other possible ways.

   It is important to note that there are 'good' bots.  Such 'good' bots
   are often found in such environments such as gaming and Internet
   Relay Chat (IRC) [RFC1459], where a continual, interactive presence
   can be a requirement for participating in the games, interacting with
   a computing resource.  Since such 'good' bots are performing useful,
   lawful, and non-disruptive functions, there is no reason for a
   provider to monitor for their presence and/or alert users to their
   presence.

   Thus, while there may be good, or harmless bots, for the purposes of
   this document all mention of bots shall assume that the bots involved
   are malicious or potentially malicious in nature.  Such malicious
   bots shall generally be assumed to have been deployed without the
   permission or conscious understanding of a particular Internet user.
   Thus, without a user's knowledge, bots may transform the user's
   computing device into a platform from which malicious activities can
   be conducted.  In addition, included explicitly in this category are
   potentially malicious bots, which may initially appear neutral but
   may simply be waiting for remote instructions to transform and/or
   otherwise begin engaging in malicious behavior.  In general,
   installation of a malicious bot without user knowledge and consent is
   considered in most regions to be unlawful, and the activities of
   malicious bots typically involve unlawful or other maliciously
   disruptive activities.

1.2.  Bot Networks, or Botnets

   These are defined as concerted networks of bots capable of acting on
   instructions generated remotely.  The malicious activities are either
   focused on the information on the local machine or acting to provide
   services for remote machines.  Bots are highly customizable so they



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   can be programmed to do many things.  The major malicious activities
   include but are not limited to: identity theft, spam, spim (spam over
   instant messaging), spit (spam over Internet telephony), email
   address harvesting, distributed denial of service (DDoS) attacks,
   key-logging, fraudulent DNS pharming (redirection), hosting proxy
   services, fast flux (see Section 1.5) hosting, hosting of illegal
   content, use in man-in-the-middle attacks, and click fraud.

   Infection vectors (infection pathways) include un-patched operating
   systems, software vulnerabilities (which include so-called zero-day
   vulnerabilities where no patch yet exists), weak/non-existent
   passwords, malicious websites, un-patched browsers, malware,
   vulnerable helper applications, inherently insecure protocols,
   protocols implemented without security features switched on and
   social engineering techniques to gain access to the user's computer.
   The detection and destruction of bots is an ongoing issue and also a
   constant battle between the Internet security community and network
   security engineers on the one hand and bot developers on the other.

   Initially, some bots used IRC to communicate but were easy to
   shutdown if the command and control server was identified and
   deactivated.  Newer command and control methods have evolved, such
   that those currently employed by bot masters make them much more
   resistant to deactivation.  With the introduction of P2P
   architectures and associated protocols as well as the use of HTTP and
   other resilient communication protocols along with the widespread
   adoption of encryption, bots are considerably more difficult to
   identify and isolate from typical network usage.  As a result
   increased reliance is being placed on anomaly detection and
   behavioral analysis, both locally and remotely, to identify bots.

1.3.  Host

   An end user's host, or computer, as used in the context of this
   document, is intended to refer to a computing device that connects to
   the Internet.  This encompasses devices used by Internet users such
   as personal computers, including laptops, desktops, and netbooks, as
   well as mobile phones, smart phones, home gateway devices, and other
   end user computing devices that are connected or can connect to the
   public Internet and/or private IP networks.

   Increasingly, other household systems and devices contain embedded
   hosts which are connected to or can connect to the public Internet
   and/or private IP networks.  However, these devices may not be under
   interactive control of the Internet user, such as may be the case
   with various smart home and smart grid devices.





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1.4.  Malware

   This is short for malicious software.  In this case, malicious bots
   are considered a subset of malware.  Other forms of malware could
   include viruses and other similar types of software.  Internet users
   can sometimes cause their hosts to be infected with malware, which
   may include a bot or cause a bot to install itself, via inadvertently
   accessing a specific website, downloading a file, or other
   activities.

   In other cases, Internet-connected hosts may become infected with
   malware through externally initiated malicious activities such as the
   exploitation of vulnerabilities or the brute force guessing of access
   credentials.

1.5.  Fast Flux

   Domain Name System (DNS) Fast Fluxing occurs when a domain is bound
   in DNS using A records to multiple IP addresses, each of which has a
   very short Time To Live (TTL) value associated with it.  This means
   that the domain resolves to varying IP addresses over a short period
   of time.

   DNS Fast Flux is typically used in conjunction with proxies that are
   normally run on compromised user hosts.  These proxies route the web
   requests to the real host which serves the data being sought.The
   effect of this is to make the detection of the real host much more
   difficult and to ensure that the backend or hidden site remains up
   for as long as possible.


2.  Introduction and Problem Statement

   Hosts used by Internet users, which in this case are customers of an
   Internet Service Provider (ISP), can be infected with malware that
   may contain and/or install one or more bots on a host.  They can
   present a major problem for an ISP for a number of reasons (not to
   mention of course the problems created for users).  First, these bots
   can be used to send spam, in some cases very large volumes of spam
   [Spamalytics].  This spam can result in extra cost for the ISPs in
   terms of wasted network, server, and/or personnel resources, among
   many other potential costs and side effects.  Such spam can also
   negatively affect the reputation of the ISP, their customers, and the
   email reputation of the IP address space used by the ISP (often
   referred to simply as 'IP reputation') A further potential
   complication is that IP space compromised by bad reputation may
   continue to carry this bad reputation even when used for entirely
   innocent purposes following re-assignment of that IP space..



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   In addition, these bots can act as platforms for directing,
   participating in, or otherwise conducting attacks on critical
   Internet infrastructure [Threat-Report].  Bots are frequently used as
   part of coordinated Distributed Denial of Service (DDoS) attacks for
   criminal, political or other motivations [Gh0st] [Dragon] [DDoS].
   For example, bots have been used to attack Internet resources and
   infrastructure ranging from web sites to email servers and DNS
   servers, as well as the critical Internet infrastructure of entire
   countries [Estonia] [Combat-Zone].  Motivations for such coordinated
   DDoS attacks can range from criminal extortion attempts through to
   online protesting and nationalistic fervor [Whiz-Kid].  DDoS attacks
   may also be motivated by simple personal vendettas or simply persons
   seeking a cheap thrill at the expense of others.

   There is good evidence to suggest that bots are being used in the
   corporate environment for purposes of corporate espionage including
   the exfiltration of corporate financial data and intellectual
   property.  This also extends to the possibility of bots being used
   for state sponsored purposes such as espionage.

   While any computing device can be infected with bots, the majority of
   bot infections affect the personal computers used by Internet end
   users.  As a result of the role of ISPs in providing IP connectivity,
   among many other services, to Internet users, these ISPs are in a
   unique position to be able to attempt to detect and observe botnets
   operating in their networks.  Furthermore, ISPs may also be in a
   unique position to be able to notify their customers of actual,
   potential, or likely infection by bots or other infection.

   From end users' perspectives, being notified that they may have an
   infected computer on their network is important information.  Once
   they know this, they can take steps to remove the bots, resolve any
   problems which may stem from the bot infection, and protect
   themselves against future threats.  Given that bots can consume vast
   amounts of local computing and network resources, enable theft of
   personal information (including personal financial information),
   enable the host to be used for criminal activities (that may result
   in the Internet user being legally culpable), destroy or leave the
   host in an unrecoverable state via 'kill switch' bot technologies, it
   is important to notify the user that they may be infected with a bot.

   As a result, the intent of this document is to provide guidance to
   ISPs and other organizations for the remediation of hosts infected
   with bots, so as to reduce the size of botnets and minimize the
   potential harm that bots can inflict upon Internet infrastructure
   generally, as well as on individual Internet users.  Efforts by ISPs
   and other organizations can, over time, reduce the pool of hosts
   infected with bots on the Internet, which in turn could result in



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   smaller botnets with less capability for disruption.

   The potential mitigation of bots is accomplished through a process of
   detection, notification to Internet users, and remediation of bot
   infections with a variety of tools, as described later in this
   document.


3.  Important Notice of Limitations and Scope

   The techniques described in this document in no way guarantee the
   remediation of all bots.  Bot removal is potentially a task requiring
   specialized knowledge, skills and tools, and may be beyond the
   ability of average users.  Attempts at bot removal may frequently be
   unsuccessful, or only partially successful, leaving the user's system
   in an unstable and unsatisfactory state or even in a state where it
   is still infected.  Attempts at bot removal can result in side
   effects ranging from a loss of data to partial or complete loss of
   system usability.

   In general, the only way a user can be sure they have removed some of
   today's increasingly sophisticated malware is by 'nuking-and-paving'
   the system: reformatting the drive, reinstalling the operating system
   and applications (including all patches) from scratch, and then
   restoring user files from a known clean backup.  However the
   introduction of persistent memory based malware may mean that, in
   some cases, this may not be enough and may prove to be more than any
   end user can be reasonably expected to resolve [BIOS].  Experienced
   users would have to re-flash or re-image persistent memory sections
   or components of their hosts in order to remove persistent memory
   based malware.  However, in some cases, not even 'nuking-and-paving'
   the system will solve the problem, which calls for hard drive
   replacement and/or complete replacement of the host.

   Devices with embedded operating systems, such as video gaming
   consoles and smart home appliances, will most likely be beyond a
   user's capability to remediate by themselves, and could therefore
   require the aid of vendor-specific advice, updates and tools.
   However, in some cases, such devices will have a function or switch
   to enable the user to reset that device to a factory default
   configuration, which may in some cases enable the user to remediate
   the infection.  Care should be taken when imparting remediation
   advice to Internet users given the increasingly wide array of
   computing devices that can be, or could be, infected by bots in the
   future.

   This document is not intended to address the issues relating to the
   prevention of bots on an end user device.  This is out of scope for



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   this document.


4.  Detection of Bots

   An ISP must first identify that an Internet user, in this case a user
   that is assumed to be their customer or otherwise connected to the
   ISP's network, is infected, or likely to have been infected with a
   bot.  The ISP should attempt to detect the presence of bots using
   methods, processes and tools that maintain the privacy of the
   personally identifiable information (PII) of their customers.  The
   ISP should not block legitimate traffic in the course of bot
   detection, and should instead employ detection methods, tools, and
   processes that seek to be non-disruptive and transparent to Internet
   users and end-user applications.

   Detection methods, tools and processes may include analysis of
   specific network and/or application traffic flows (such as traffic to
   an email server), analysis of aggregate network and/or application
   traffic data, data feeds received from other ISPs and organizations
   (such as lists of the ISP's IP addresses which have been reported to
   have sent spam), feedback from the ISP's customers or other Internet
   users, as well as a wide variety of other possibilities.  In
   practice, it has proven effective to confirm a bot infection through
   the use of a combination of multiple bot detection data points.  This
   can help to corroborate information of varying dependability or
   consistency, as well as to avoid or minimize the possibility of false
   positive identification of hosts.  Detection should also, where
   possible and feasible, attempt to classify the specific bot infection
   type in order to confirm that it is malicious in nature, estimate the
   variety and severity of threats it may pose (such as spam bot, key-
   logging bot, file distribution bot, etc.), and to determine potential
   methods for eventual remediation.  However, given the dynamic nature
   of botnet management and the criminal incentives to seek quick
   financial rewards, botnets frequently update or change their core
   capabilities.  As a consequence, botnets that are initially detected
   and classified by the ISP as made up of one particular type of bot
   need to be continuously monitored and tracked in order to identify
   correctly the threat the botnet poses at any particular point in
   time.

   Detection is also time-sensitive.  If complex analysis is required
   and multiple confirmations are needed to verify a bot is indeed
   present, then it is possible that the bot may cause some damage (to
   either the infected host or a remotely targeted system) before it can
   be stopped.  This means that an ISP needs to balance the desire or
   need to definitively classify and/or confirm the presence of a bot,
   which may take an extended period of time, with the ability to



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   predict the likelihood of a bot in a very short period of time.  Such
   determinations must have a relatively low false positive rate in
   order to maintain the trust of users.  This 'definitive-vs-likely'
   challenge is difficult and, when in doubt, ISPs should err on the
   side of caution by communicating that a bot infection has taken
   place.  This also means that Internet users may benefit from the
   installation of client-based security software on their host.  This
   can enable rapid heuristically-based detection of bot activity, such
   as the detection of a bot as it starts to communicate with other
   botnets and execute commands.  Any bot detection system should also
   be capable of adapting, either via manual intervention or
   automatically, in order to cope with a rapidly evolving threat.

   As noted above, detection methods, tools, and processes should ensure
   that privacy of customers' personally identifiable information (PII)
   is maintained.  This protection afforded to PII should also extend to
   third parties processing data on behalf of ISPs.  While bot detection
   methods, tools, and processes are similar to spam and virus defenses
   deployed by the ISP for the benefit of their customers (and may be
   directly related to those defenses), attempts to detect bots should
   take into account the need of an ISP to take care to ensure any PII
   collected or incidentally detected is properly protected.  This is
   important, as just as spam defenses may involve scanning the content
   of email messages, which may contain PII, then so too may bot
   defenses similarly come into incidental contact with PII.  The
   definition of PII varies from one jurisdiction to the next so proper
   care should be taken to ensure that any actions taken comply with
   legislation and good practice in the jurisdiction in which the PII is
   gathered.  Finally, depending upon the geographic region within which
   an ISP operates, certain methods relating to bot detection may need
   to be included in relevant terms of service documents or other
   documents which are available to the customers of a particular ISP.

   There are several bot detection methods, tools, and processes that an
   ISP may choose to utilize, as noted in the list below.  It is
   important to note that the technical solutions available are
   relatively immature, and are likely to change over time, evolving
   rapidly in the coming years.  While these items are described in
   relation to ISPs, they may also be applicable to organizations
   operating other networks, such as campus networks and enterprise
   networks.

   a.  Where it is not legally proscribed and an accepted industry
       practice in a particular market region, an ISP may in some manner
       "scan" its IP space in order to detect un-patched or otherwise
       vulnerable hosts, or to detect the signs of infection.  This may
       provide the ISP with the opportunity to easily identify Internet
       users who appear to already be infected or are at great risk of



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       being infected with a bot.  ISPs should note that some types of
       port scanning may leave network services in a hung state or
       render them unusable due to common frailties, and that many
       modern firewall and host-based intrusion detection
       implementations may alert the Internet user to the scan.  As a
       result the scan may be interpreted as a malicious attack against
       the host.  Vulnerability scanning has a higher probability of
       leaving accessible network services and applications in a damaged
       state and will often result in a higher probability of detection
       by the Internet user and subsequent interpretation as a targeted
       attack.  Depending upon the vulnerability for which an ISP may be
       scanning, some automated methods of vulnerability checking may
       result in data being altered or created afresh on the Internet
       user's host which can be a problem in many legal environments.
       It should also be noted that due to the prevalence of Network
       Address Translation devices, Port Address Translation devices,
       and/or firewall devices in user networks, network-based
       vulnerability scanning may be of limited value.  Thus, while we
       note that this is one technique that may be utilized, it is
       unlikely to be particularly effective and it has problematic side
       effects, which leads the authors to recommend against the use of
       this particular method.

   b.  An ISP may also communicate and share selected data, via feedback
       loops or other mechanisms, with various third parties.  Feedback
       loops are consistently formatted feeds of real-time (or nearly
       real-time) abuse reports offered by threat data clearinghouses,
       security alert organizations, other ISPs, and other
       organizations.  The formats for feedback loops include those
       defined in both ARF [RFC5965] and IODEF [RFC5070].  The data may
       include, but is not limited to, IP addresses of hosts that appear
       to be either definitely or probably infected, IP addresses,
       domain names or fully qualified domain names (FQDNs) known to
       host malware and/or be involved in the command and control of
       botnets, recently tested or discovered techniques for detecting
       or remediating bot infections, new threat vectors, and other
       relevant information.  A few good examples of data sharing are
       noted in Appendix A.

   c.  An ISP may use Netflow [RFC3954] or other similar passive network
       monitoring to identify network anomalies that may be indicative
       of botnet attacks or bot communications.  For example, an ISP may
       be able to identify compromised hosts by identifying traffic
       destined to IP addresses associated with the command and control
       of botnets, or destined to the combination of an IP address and
       control port associated with a command and control network
       (sometimes command and control traffic comes from a host which
       has legitimate traffic).  In addition, bots may be identified



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       when a remote host is under a DDoS attack, because hosts
       participating in the attack will likely be infected by a bot,
       frequently as observed at network borders (though ISPs should
       beware of source IP address spoofing techniques to avoid or
       confuse detection).

   d.  An ISP may use DNS-based techniques to perform detection.  For
       example, a given classified bot may be known to query a specific
       list of domain names at specific times or on specific dates (in
       the example of the so-called "Conficker" bot (see [Conficker]),
       often by matching DNS queries to a well known list of domains
       associated with malware.  In many cases such lists are
       distributed by or shared using third parties, such as threat data
       clearinghouses.

   e.  User complaints: Because hosts infected by bots are frequently
       used to send spam or participate in DDoS attacks, the ISP
       servicing those hosts will normally receive complaints about the
       malicious network traffic.  Those complaints may be sent to
       RFC2142-specified [RFC2142] role accounts, such as abuse@, or to
       other relevant addresses such as to abuse or security addresses
       specified by the site as part of its WHOIS (or other) contact
       data.

   f.  ISPs may also discover likely bot infected hosts located on other
       networks.  Thus, when legally permissible in a particular market
       region, it may be worthwhile for ISPs to share information
       relating to those compromised hosts with the relevant remote
       network operator, with security researchers, and with blocklist
       operators.

   g.  ISPs may operate or subscribe to services that provide
       'sinkholing' or 'honeynet' capabilities.  This may enable the ISP
       to obtain near-real-time lists of bot infected hosts as they
       attempt to join a larger botnet or propagate to other hosts on a
       network.

   h.  ISP industry associations should examine the possibility of
       collating statistics from ISP members in order to provide good
       statistics about bot infections based on real ISP data.

   i.  An Intrusion Detection System (IDS) can be a useful tool to
       actually help identify the malware.  An IDS tool such as SNORT
       (open source IDS platform; see [Snort]) can be placed in a Walled
       Garden and used to analyze end user traffic to confirm malware
       type.  This will help with remediation of the infected device.





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5.  Notification to Internet Users

   Once an ISP has detected a bot, or the strong likelihood of a bot,
   steps should be undertaken to inform the Internet user that they may
   have a bot-related problem.  Depending upon a range of factors
   including technical capabilities of the ISP, technical attributes of
   its network, financial considerations, available server resources,
   available organizational resources, the number of likely infected
   hosts detected at any given time and the severity of any possible
   threats, among other things, an ISP should decide the most
   appropriate method or methods for providing notification to one or
   more of their customers or Internet users.  Such notification methods
   may include one or more of the methods described in the following
   subsections, as well as other possible methods not described below.

   It is important to note that none of these methods are guaranteed to
   be one-hundred percent successful, and that each has its own set of
   limitations.  In addition, in some cases, an ISP may determine that a
   combination of two or more methods is most appropriate and effective,
   and reduces the chance that malware may block a notification.  As
   such, the authors recommend the use of multiple notification methods.
   Finally, notification is also considered time sensitive; if the user
   does not receive or view the notification in a timely fashion, then a
   particular bot could launch an attack, exploit the user, or cause
   other harm.  If possible, an ISP should establish a preferred means
   of communication when the subscriber first signs up for service.  As
   a part of the notification process, ISPs should maintain a record of
   the allocation of IP addresses to subscribers for such a period long
   enough to allow any commonly used bot detection technology to be able
   to accurately link an infected IP address to a subscriber.  This
   record should only be maintained for a period of time which is
   necessary to support bot detection,but no longer, in order to protect
   the privacy of the individual subscriber.

   One important factor to bear in mind is that notification to end
   users needs to be resistant to potential spoofing.  This should be
   done to protect, as reasonably as possible, against the potential of
   legitimate notifications being spoofed and/or used by parties with
   intent to perform additional malicious attacks against victims of
   malware, or even to deliver additional malware.

   It should be possible for the end user to indicate the preferred
   means of notification on an opt-in basis for that notification
   method.  It is recommended that the end user should not be allowed to
   opt out of notification entirely.

   When users are notified, an ISP should endeavor to give as much
   information to the end user regarding which bot detection methods



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   employed at the ISP consonant with not providing information to those
   creating or deploying the bots so that they would be able to avoid
   detection.

5.1.  Email Notification

   This is a common form of notification used by ISPs.  One drawback of
   using email is that it is not guaranteed to be viewed within a
   reasonable time frame, if at all.  The user may be using a different
   primary email address than that which they have provided to the ISP.
   In addition, some ISPs do not provide an email account at all, as
   part of a bundle of Internet services, and/or do not have a need for
   or method by which to request or retain the primary email addresses
   of Internet users of their networks.  Another possibility is that the
   user, their email client, and/or their email servers could determine
   or classify such a notification as spam, which could delete the
   message or otherwise file it in an email folder that the user may not
   check on a regular and/or timely basis.  Bot masters have also been
   known to impersonate the ISP or trusted sender and send fraudulent
   emails to the users.  This technique of social engineering often
   leads to new bot infestations.  Finally if the user's email
   credentials are compromised, then a hacker and/or a bot could simply
   access the user's email account and delete the email before it is
   read by the user.

5.2.  Telephone Call Notification

   A telephone call may be an effective means of communication in
   particularly high-risk situations.  However, telephone calls may not
   be feasible due to the cost of making a large number of calls, as
   measured in either time, money, organizational resources, server
   resources, or some other means.  In addition, there is no guarantee
   that the user will answer their phone.  To the extent that the
   telephone number called by the ISP can be answered by the infected
   computing device, the bot on that host may be able to disconnect,
   divert, or otherwise interfere with an incoming call.  Users may also
   interpret such a telephone notification as a telemarketing call and
   as such not welcome it, or not accept the call at all.  Finally, even
   if a representative of the ISP is able to connect with and speak to a
   user, that user is very likely to lack the necessary technical
   expertise to understand or be able to effectively deal with the
   threat.

5.3.  Postal Mail Notification

   This form of notification is probably the least popular and effective
   means of communication, due to both preparation time, delivery time,
   the cost of printing and paper, and the cost of postage.



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5.4.  Walled Garden Notification

   Placing a user in a walled garden is another approach that ISPs may
   take to notify users.  A walled garden refers to an environment that
   controls the information and services that a subscriber is allowed to
   utilize and what network access permissions are granted.  A walled
   garden implementation can range from strict to leaky.  In a strict
   walled garden environment, access to most Internet resources is
   typically limited by the ISP.  In contrast, a leaky walled garden
   environment permits access to all Internet resources, except those
   deemed malicious, and ensures access to those that can be used to
   notify users of infections.

   Walled gardens are effective because it is possible to notify the
   user and simultaneously block all communication between the bot and
   the command and control channel.  While in many cases the user is
   almost guaranteed to view the notification message and take any
   appropriate remediation actions, this approach can pose other
   challenges.  For example, it is not always the case that a user is
   actively using a host that uses a web browser or that has a web
   browser actively running on it, or that uses another application
   which uses ports which are redirected to the walled garden.  In one
   example, a user could be playing a game online, via the use of a
   dedicated, Internet-connected game console.  In another example, the
   user may not be using a host with a web browser when they are placed
   in the walled garden and may instead be in the course of a telephone
   conversation, or may be expecting to receive a call, using a Voice
   Over IP (VoIP) device of some type.  As a result, the ISP may feel
   the need to maintain a potentially lengthy white list of domains that
   are not subject to the typical restrictions of a walled garden, which
   could well prove to be an onerous task from an operational
   perspective.

   For these reasons the implementation of a leaky walled garden makes
   more sense, but a leaky walled garden has a different set of
   drawbacks.  The ISP has to assume that the user will eventually use a
   web browser to acknowledge the notification, otherwise the user will
   remain in the walled garden and not know it.  If the intent of the
   leaky walled garden is solely to notify the user about the bot
   infection, then the leaky walled garden is not ideal because
   notification is time sensitive and the user may not receive the
   notification until the user invokes a request for the targeted
   service and/or resource.  This means the bot can potentially do more
   damage.  Additionally, the ISP has to identify which services and/or
   resources to restrict for the purposes of notification.  This does
   not have to be resource specific and can be time based and/or policy
   based.  An example of how notification could be made on a timed basis
   could involve notification for all HTTP requests every 10 minutes, or



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   show the notification for one in five HTTP requests.

   The ISP has several options to determine when to let the user out of
   the walled garden.  One approach may be to let the user determine
   when to exit.  This option is suggested when the primary purpose of
   the walled garden is to notify users and provide information on
   remediation only, particularly since notification is not a guarantee
   of successful remediation.  It could also be the case that, for
   whatever reason, the user makes the judgment that they cannot then
   take the time to remediate their host and that other online
   activities which they would like to resume are more important.  Exit
   from the walled garden may also involve a process to verify that it
   is indeed the user who is requesting exit from the walled garden and
   not the bot.

   Once the user acknowledges the notification, they may decide to
   either remediate and exit the walled garden or to exit the walled
   garden without remediating the issue.  Another approach may be to
   enforce a stricter policy and require the user to clean the host
   prior to permitting the user to exit the walled garden, though this
   may not be technically feasible depending upon the type of bot,
   obfuscation techniques employed by a bot, and/or a range of other
   factors.  Thus, the ISP may also need to support tools to scan the
   infected host (in the style of a virus scan, rather than a port scan)
   and determine whether it is still infected or rely on user judgment
   that the bot has been disabled or removed.  One challenge with this
   approach is that the user might have multiple hosts sharing a single
   IP address, such as via a common home gateway device which performs
   Network Address Translation (NAT).  In such a case, the ISP may need
   to determine from user feedback, or other means, that all affected
   hosts have been remediated, which may or may not be technically
   feasible.

   Finally, when a walled garden is used, a list of well-known addresses
   for both operating system vendors and security vendors should be
   created and maintained in a white list which permits access to these
   sites.  This can be important for allowing access from the walled
   garden by end users in search of operating system and application
   patches.  It is recommended that walled gardens be seriously
   considered as a method of notification as they are easy to implement
   and proven to be effective as a means of getting end user attention.

5.5.  Instant Message Notification

   Instant messaging provides the ISP with a simple means to communicate
   with the user.  There are several advantages to using Instant
   Messaging (IM) that make it an attractive option.  If the ISP
   provides IM service and the user subscribes to it, then the user can



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   be notified easily.  IM-based notification can be a cost effective
   means to communicate with users automatically from an IM alert system
   or by a manual process, involving the ISP's support staff.  Ideally,
   the ISP should allow the user to register their IM identity in an ISP
   account management system and grant permission to be contacted via
   this means.  If the IM service provider supports off-line messaging,
   then the user can be notified regardless of whether they are
   currently logged into the IM system.

   There are several drawbacks with this communications method.  There
   is a high probability that subscriber may interpret the communication
   to be spim, and as such ignore it.  Also, not every user uses IM
   and/or the user may not provide their IM identity to the ISP so some
   alternative means have to be used.  Even in those cases where a user
   does have an IM address, they may not be signed onto that IM system
   when the notification is attempted.  There may be a privacy concern
   on the part of users, when such an IM notification must be
   transmitted over a third-party network and/or IM service.  As such,
   should this method be used, the notification should be discreet and
   not include any PII in the notification itself.

5.6.  Short Message Service (SMS) Notification

   SMS allows the ISP to send a brief description of the problem to
   notify the user of the issue, typically to a mobile device such as a
   mobile phone or smart phone.  Ideally, the ISP should allow the user
   to register their mobile number and/or SMS address in an ISP account
   management system and grant permission to be contacted via this
   means.  The primary advantage of SMS is that users are familiar with
   receiving text messages and are likely to read them.  However, users
   may not act on the notification immediately if they are not in front
   of their host at the time of the SMS notification.

   One disadvantage is that ISPs may have to follow up with an alternate
   means of notification if not all of the necessary information may be
   conveyed in one message, given constraints on the number of
   characters in an individual message (typically 140 characters).
   Another disadvantage with SMS is the cost associated with it.  The
   ISP has to either build its own SMS gateway to interface with the
   various wireless network service providers or use a third-party SMS
   clearinghouse (relay) to notify users.  In both cases an ISP may
   incur fees related to SMS notifications, depending upon the method
   used to send the notifications.  An additional downside is that SMS
   messages sent to a user may result in a charge to the user by their
   wireless provider, depending upon the plan to which they subscribe
   and the country in which the user resides.  Another minor
   disadvantage is that it is possible to notify the wrong user if the
   intended user changes their mobile number but forgets to update it



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   with the ISP.

   There are several other drawbacks with this communications method.
   There is a high probability that subscriber may interpret the
   communication to be spam, and as such ignore it.  Also, not every
   user uses SMS and/or the user may not provide their SMS address or
   mobile number to the ISP.  Even in those cases where a user does have
   an SMS address or mobile number, their device may not be powered on
   or otherwise available on a wireless network when the notification is
   attempted.  There maybe also be a privacy concern on the part of
   users, when such an SMS notification must be transmitted over a
   third-party network and/or SMS clearinghouse.  As such, should this
   method be used, the notification should be discreet and not include
   any PII in the notification itself.

5.7.  Web Browser Notification

   Near real-time notification to the user's web browser is another
   technique that may be utilized for notifying the user [RFC6108],
   though how such a system might operate is outside the scope of this
   document.  Such a notification could have a comparative advantage
   over a walled garden notification, in that it does not restrict
   traffic to a specified list of destinations in the same way that a
   walled garden by definition would.  However, as with a walled garden
   notification, there is no guarantee that a user is at any given time
   making use of a web browser, though such a system could certainly
   provide a notification when such a browser is eventually used.
   Compared to a walled garden, a web browser notification is probably
   preferred from the perspective of Internet users, as it does not have
   the risk of disrupting non-web sessions, such as online games, VoIP
   calls, etc. (as noted in Section 5.4).

   There are alternative methods of web browser notification offered
   commercially by a number of vendors.  Many of the techniques used are
   proprietary and it is not within the scope of this document to
   describe how they are implemented.  These techniques have been
   successfully implemented at several ISPs.

   It should be noted that web notification is only intended to notify
   devices running a web browser.

5.8.  Considerations for Notification to Public Network Locations

   Delivering a notification to a location that provides a shared public
   network, such as a train station, public square, coffee shop, or
   similar location may be of low value since the users connecting to
   such networks are typically highly transient and generally not known
   to site or network administrators.  For example, a system may detect



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   that a host on such a network has a bot, but by the time a
   notification is generated that user has departed from the network and
   moved elsewhere.

5.9.  Considerations for Notification to Network Locations Using a
      Shared IP Address

   Delivering a notification to a location that accesses the Internet
   routed through one or more shared public IP addresses may be of low
   value since it may be quite difficult to differentiate between users
   when providing a notification.  For example, on a business network of
   500 users, all sharing one public IP address, it may be sub-optimal
   to provide a notification to all 500 users if you only need one
   specific user to be notified and take action.  As a result, such
   networks may find value in establishing a localized bot detection and
   notification system, just as they are likely to also establish other
   localized systems for security, file sharing, email, and so on.

   However, should an ISP implement some form of notification to such
   networks, it may be better to simply send notifications to a
   designated network administrator at the site.  In such a case the
   local network administrator may like to receive additional
   information in such a notification, such as a date and timestamp, the
   source port of the infected system, and malicious sites and ports
   that may have been visited.

5.10.  Notification and End User Expertise

   The ultimate effectiveness of any of the aforementioned forms of
   notification is heavily dependent upon both the expertise of the end
   user and the wording of any such notification.  For example, while a
   user may receive and acknowledge a notification, that user may lack
   the necessary technical expertise to understand or be able to deal
   effectively with the threat.  As a result, it is important that such
   notifications use clear and easily understood language, so that the
   majority of users (who are non-technical) may understand the
   notification.  In addition, a notification should provide easily
   understood guidance on how to remediate a threat as described in
   Section 6, potentially with one path for technical users to take and
   another for non-technical users.


6.  Remediation of Hosts Infected with a Bot

   This section covers the different options available to remediate a
   host, which means to remove, disable, or otherwise render a bot
   harmless.  Prior to this step, an ISP has detected the bot, notified
   the user that one of their hosts is infected with a bot, and now may



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   provide some recommended means to clean the host.  The generally
   recommended approach is to provide the necessary tools and education
   to the user so that they may perform bot remediation themselves,
   particularly given the risks and difficulties inherent in attempting
   to remove a bot.

   For example, this may include the creation of a special web site with
   security-oriented content that is dedicated for this purpose.  This
   should be a well-publicized security web site to which a user with a
   bot infection can be directed to for remediation.  This security web
   site should clearly explain why the user was notified and may include
   an explanation of what bots are, and the threats that they pose.
   There should be a clear explanation of the steps that the user should
   take in order to attempt to clean their host and provide information
   on how users can keep the host free of future infections.  The
   security web site should also have a guided process that takes non-
   technical users through the remediation process, on an easily
   understood, step-by-step basis.

   In terms of the text used to explain what bots are and the threats
   that they pose, something simple such as this may suffice:

         "What is a bot?  A bot is a piece of software, generally
         installed on your machine without your knowledge, which either
         sends spam or tries to steal your personal information.  They
         can be very difficult to spot, though you may have noticed that
         your computer is running much more slowly than usual or you
         notice regular disk activity even when you are not doing
         anything.  Ignoring this problem is risky to you and your
         personal information.  Thus, bots need to be removed to protect
         your data and your personal information."

   Many bots are designed to work in a very stealthy manner and as such
   there may be a need to make sure that the Internet user understands
   the magnitude of the threat faced despite the stealthy nature of the
   bot.

   It is also important to note that it may not be immediately apparent
   to the Internet user precisely which devices have been infected with
   a particular bot.  This may be due to the user's home network
   configuration, which may encompass several hosts, where a home
   gateway which performs Network Address Translation (NAT) to share a
   single public IP address has been used.  Therefore, any of these
   devices can be infected with a bot.  The consequence of this for an
   ISP is that remediation advice may not ultimately be immediately
   actionable by the Internet user, as that user may need to perform
   additional investigation within their own home network.




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   An added complication is that the user may have a bot infection on a
   device such as a video console, multimedia system, appliance, or
   other end-user computing device which does not have a typical desktop
   computing interface.  As a result, diligence needs to be taken by the
   ISP where possible such that it can identify and communicate the
   specific nature of the device that has been infected with a bot, and
   further providing appropriate remediation advice.  If the ISP cannot
   pin down the device or identify its type, then it should make it
   clear to the user that any initial advice given is generic and
   further advice can be given (or is available) once the type of
   infected device is known.

   There are a number of forums that exist online to provide security
   related support to end users.  These forums are staffed by volunteers
   and often are focussed around the use of a common tool set to help
   end users to remediate hosts infected with malware.  It may be
   advantageous to ISPs to foster a relationship with one or more
   forums, perhaps by offering free hosting or other forms of
   sponsorship.

   It is also important to keep in mind that not all users will be
   technically adept as noted in Section 5.10.  As a result, it may be
   more effective to provide a range of suggestion options for
   remediation.  This may include for example a very detailed "do it
   yourself" approach for experts, a simpler guided process for the
   average user, and even assisted remediation as described in
   Section 6.2.

6.1.  Guided Remediation Process

   Minimally, the Guided Remediation Process should include the
   following goals, with options and/or recommendations for achieving
   them:

   1.  Backup personal files.  For example: "Before you start, make sure
       to backup all of your important data.  (You should do this on a
       regular basis anyway.)  You can backup your files manually or
       using a system backup software utility, which may be part of your
       Operating System (OS).  You can backup your files to a USB Thumb
       Drive (aka USB Key), a writeable CD/DVD-ROM, an external hard
       drive, a network file server, or an Internet-based backup
       service."  It may be advisable to suggest that the user backup is
       performed onto separate backup media or devices if they suspect
       bot infection.

   2.  Download OS patches and Anti-Virus (A/V) software updates.  For
       example, links could be provided to Microsoft Windows updates as
       well as to Apple MacOS updates, or to other major operating



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       systems which are relevant to users and their devices.

   3.  Configure the host to automatically install updates for the OS,
       A/V and other common Web Browsers such as Microsoft Internet
       Explorer, Mozilla Firefox, Apple Safari, Opera, and Google
       Chrome.

   4.  Get professional assistance if they are unable to remove the bots
       themselves.  If purchasing professional assistance, then the user
       should be encouraged to pre-determine how much they are willing
       to pay for that help.  If the host that is being remediated is
       old and can easily be replaced with a new, faster, larger and
       more reliable system for a certain cost, the it makes no sense to
       spend more than that cost to fix the old host, for example.  On
       the other hand, if the customer has a brand new host, it might
       make perfect sense to spend the money to attempt to remediate it.

   5.  To continue, regardless of whether the user or a knowledgeable
       technical assistant is working on remediating the host, their
       first task should be to determine which of multiple potentially-
       infected machines may be the one that needs attention (in the
       common case of multiple hosts in a home network).  Sometimes, as
       in cases where there is only a single directly-attached host, or
       the user has been noticing problems with one of their hosts, this
       can be easy.  Other times, it may be more difficult especially if
       there are no clues as to which host is infected.  If the user is
       behind a home gateway/router, then the first task may be to
       ascertain which of the machines is infected.  In some cases the
       user may have to check all machines to identify the infected one.

   6.  ISPS may also look at offering a CD/DVD with remediation
       processes and software in the event that a host is so badly
       infected as to be unable to communicate over the Internet.

   7.  User surveys to solicit feedback on whether the notification and
       remediation process is effective and what recommended changes
       could be made in order to improve the ease, understandability,
       and effectiveness the remediation process.

   8.  If the user is interested in reporting his or her host's bot
       infection to an applicable law enforcement authority, then the
       host effectively becomes a cyber "crime scene" and the infection
       should not be mitigated unless or until law enforcement has
       collected the necessary evidence.  For individuals in this
       situation, the ISP may wish to provide links to local, state,
       federal, or other relevant computer crime offices.  (Note: Some
       "minor" incidents, even if highly traumatic to the user, may not
       be sufficiently serious for law enforcement to commit some of



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       their limited resources to an investigation.)  In addition,
       individual regions may have other, specialized computer crime
       organizations to which these incidents can be reported.  For
       example, in the United States, that organization is the Internet
       Crime Complaint Center, at http://www.ic3.gov.

   9.  Users may also be interested in links to security expert forums,
       where other users can assist them.

6.2.  Professionally-Assisted Remediation Process

   It should be acknowledged that, based on the current state of
   remediation tools and the technical abilities of end users, that many
   users may be unable to remediate on their own.  As a result, it is
   recommended that users have the option for professional assistance.
   This may entail online or telephone assistance for remediation, as
   well as working face to face with a professional who has training and
   expertise in the removal of malware.  It should be made clear at the
   time of offering this service that this service is intended for those
   that do not have the skills or confidence to attempt remediation and
   is not intended as an up-sell by the ISP.


7.  Failure or Refusal to Remediate

   ISP systems should track the bot infection history of hosts in order
   to detect when users consistently fail to remediate or refuse to take
   any steps to remediate.  In such cases, ISPs may need to consider
   taking additional steps to protect their network, other users and
   hosts on that network, and other networks.  Such steps may include a
   progression of actions up to and including account termination.
   Refusal to remediate can be viewed as a business issue and as such no
   technical recommendation is possible.


8.  Sharing of Data from the User to the ISP

   As an additional consideration, it may be useful to create a process
   by which users could choose, at their option and with their express
   consent, to share data regarding their bot infections with their ISP
   and/or another authorized third party.  Such third parties may
   include governmental entities that aggregate threat data, such as the
   Internet Crime Complaint Center referred to earlier in this document,
   to academic institutions, and/or security researchers.  While in many
   cases the information shared with the user's ISP or designated third
   parties will only be used for aggregated statistical analysis, it is
   also possible that certain research needs may be best met with more
   detailed data.  Thus, any such data sharing from a user to the ISP or



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   authorized third party may contain some type of personally
   identifiable information, either by design or inadvertently.  As a
   result, any such data sharing should be enabled on an opt-in basis,
   where users review and approve of the data being shared and the
   parties with which it is to be shared, unless the ISP is already
   required to share such data in order to comply with local laws and in
   accordance with those laws and applicable regulations.


9.  Security Considerations

   This document describes in detail the numerous security risks and
   concerns relating to botnets.  As such, it has been appropriate to
   include specific information about security in each section above.
   This document describes the security risks related to malicious bot
   infections themselves, such as enabling identity theft, theft of
   authentication credentials, and the use of a host to unwittingly
   participate in a DDoS attack, among many other risks.  Finally, the
   document also describes security risks which may relate to the
   particular methods of communicating a notification to Internet users.
   Bot networks and bot infections pose extremely serious security risks
   and any reader should review this document carefully.

   In addition, regarding notifications, as described in Section 5, care
   should be taken to assure users that notifications have been provided
   by a trustworthy site and/or party, so that the notification is more
   difficult for phishers and/or malicious parties using social
   engineering tactics to mimic, or that the user has some level of
   trust that the notification is valid, and/or that the user has some
   way to verify via some other mechanism or step that the notification
   is valid.


10.  Privacy Considerations

   This document describes at a high level the activities to which ISPs
   should be sensitive, where the collection or communication of PII may
   be possible.  In addition, when performing notifications to end users
   Section 5, those notifications should not include PII.

   As noted in Section 8, any sharing of data from the user to the ISP
   and/or authorized third parties should be done on an opt-in basis.
   Additionally the ISP and or authorized third parties should clearly
   state what data will be shared and with whom the data will be shared.

   Lastly, as noted in some other sections, there my be legal
   requirements in particular legal jurisdictions concerning how long
   any subscriber-related or other data is retained, of which an ISP



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   operating in such a jurisdiction should be aware and with which an
   ISP should comply.


11.  IANA Considerations

   There are no IANA considerations in this document.


12.  Acknowledgements

   The authors wish to acknowledge the following individuals and groups
   for performing a detailed review of this document and/or providing
   comments and feedback that helped to improve and evolve this
   document:

   Mark Baugher

   Richard Bennett

   James Butler

   Vint Cerf

   Alissa Cooper

   Jonathan Curtis

   Jeff Chan

   Roland Dobbins

   Dave Farber

   Stephen Farrell

   Eliot Gillum

   Joel Halpern

   Joel Jaeggli

   Scott Keoseyan

   Murray S. Kucherawy

   The Messaging Anti-Abuse Working Group (MAAWG)




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   Jose Nazario

   Gunter Ollmann

   David Reed

   Roger Safian

   Donald Smith

   Joe Stewart

   Forrest Swick

   Sean Turner

   Robb Topolski

   Maxim Weinstein

   Eric Ziegast


13.  Informative references

   [BIOS]     Sacco, A. and A. Ortega, "Persistent BIOS Infection",
              March 2009, <http://www.coresecurity.com/files/
              attachments/Persistent_BIOS_Infection_CanSecWest09.pdf>.

   [Combat-Zone]
              Alshech, E., "Cyberspace as a Combat Zone: The Phenomenon
              of Electronic Jihad", February 2007, <http://
              www.memrijttm.org/content/en/report.htm?report=1822>.

   [Conficker]
              Porras, P., Saidi, H., and V. Yegneswaran, "An Analysis of
              Conficker's Logic and Rendezvous Points", March 2009,
              <http://mtc.sri.com/Conficker/>.

   [DDoS]     Saafan, A., "Distributed Denial of Service Attacks:
              Explanation, Classification and Suggested Solutions",
              March 2009, <www.exploit-db.com/download_pdf/14738/>.

   [Dragon]   Nagaraja, S. and R. Anderson, "The snooping dragon:
              social-malware surveillance of the Tibetan movement",
              March 2009,
              <http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-746.pdf>.




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   [Estonia]  Evron, G., "Battling Botnets and Online Mobs: Estonia's
              Defense Efforts during the Internet War", May 2005, <http:
              //docs.google.com/
              gview?a=v&
              q=cache%3AbyUMj6Djlb8J%3Awww.ciaonet.org%2Fjournals%
              2Fgjia%2Fv9i1%2F0000699.pdf>.

   [Gh0st]    Vallentin, M., Whiteaker, J., and Y. Ben-David, "The Gh0st
              in the Shell: Network Security in the Himalayas",
              February 2010, <http://www.infowar-monitor.net/wp-content/
              uploads/2010/02/cs294-28-paper.pdf>.

   [RFC1459]  Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol",
              RFC 1459, May 1993.

   [RFC2142]  Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
              FUNCTIONS", RFC 2142, May 1997.

   [RFC3954]  Claise, B., "Cisco Systems NetFlow Services Export Version
              9", RFC 3954, October 2004.

   [RFC5070]  Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
              Object Description Exchange Format", RFC 5070,
              December 2007.

   [RFC5965]  Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              August 2010.

   [RFC6108]  Chung, C., Kasyanov, A., Livingood, J., Mody, N., and B.
              Van Lieu, "Comcast's Web Notification System Design",
              RFC 6108, February 2011.

   [Snort]    Roesch, M., "Snort Home Page", March 2009,
              <http://www.snort.org/>.

   [Spamalytics]
              Kanich, C., Kreibich, C., Levchenko, K., Enright, B.,
              Voelker, G., Paxson, V., and S. Savage, "Spamalytics: An
              Empirical Analysis of Spam Marketing Conversion",
              October 2008, <http://www.icir.org/christian/publications/
              2008-ccs-spamalytics.pdf>.

   [Threat-Report]
              Ahamad, M., Amster, D., Barret, M., Cross, T., Heron, G.,
              Jackson, D., King, J., Lee, W., Naraine, R., Ollman, G.,
              Ramsey, J., Schmidt, H., and P. Traynor, "Emerging Cyber
              Threats Report for 2009: Data, Mobility and Questions of



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              Responsibility will Drive Cyber Threats in 2009 and
              Beyond", October 2008, <http://smartech.gatech.edu/
              bitstream/1853/26301/1/CyberThreatsReport2009.pdf>.

   [Whiz-Kid]
              Berinato, S., "Case Study: How a Bookmaker and a Whiz Kid
              Took On a DDOS-based Online Extortion Attack", May 2005, <
              http://www.csoonline.com/article/220336/
              How_a_Bookmaker_and_a_Whiz_Kid_Took_On_a_DDOS_based_Online
              _Extortion_Attack>.


Appendix A.  Examples of Third Party Malware Lists

   As noted in Section 4, there are many potential third parties which
   may be willing to share lists of infected hosts.  This list is for
   example purposes only, is not intended to be either exclusive or
   exhaustive, and is subject to change over time.

   o  Arbor - Atlas, see http://atlas.arbor.net/

   o  Internet Systems Consortium - Secure Information Exchange (SIE),
      see https://sie.isc.org/

   o  Microsoft - Smart Network Data Services (SNDS), see
      https://postmaster.live.com/snds/

   o  SANS Institute / Internet Storm Center - DShield Distributed
      Intrusion Detection System, see http://www.dshield.org/about.html

   o  ShadowServer Foundation, see http://www.shadowserver.org/

   o  Spamhaus - Policy Block List (PBL), see
      http://www.spamhaus.org/pbl/

   o  Spamhaus - Exploits Block List (XBL), see
      http://www.spamhaus.org/xbl/

   o  Team Cymru - Community Services, see http://www.team-cymru.org/


Appendix B.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -20 version:





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   o  Addressed comments raised at IESG ommitted in -19

   o  minor nits corrections

   -19 version:

   o  Addressed comments raised at IESG

   o  minor nits corrections

   -18 version:

   o  minor nits corrections

   -17 version:

   o  various copy editing

   o  briefly discuss IP reputation issues

   o  briefly discuss corporate espionage threat

   o  add references for ARF and IODEF, Snort, and Conficker

   -16 version:

   o  Section 6.1.6 Substituted unable for able

   -15 version:

   o  Issue of quiet bots addressed

   o  Section 5.4 substitute "may be" for maybe

   o  Section 5.4 Added reference to country of residence

   o  Section 5.8 Corrected spelling error

   o  Section 5.10 Correctedspelling error

   o  Section 6 Corrected spelling errors

   -14 version:

   o  Minor errors rectified, spelling errors addressed

   o  ALL open issues are now closed!




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   -13 version:

   o  All changes below per Sean Farrell except where indicated

   o  Section 1.2 Added reference to fast flux definition

   o  Section 1.2 Included reference to insecure protocols

   o  Section 4 Cleared ambiguity

   o  Section 4 Substituted "must have"

   o  Section 4 Substituted "to" for "too"

   o  Section 4 Addressed PII issue for 3rd parties

   o  Section 4 Addressed issue around blocking of traffic during bot
      detection process

   o  Section 5 Per Max Weinstein Included a number of comments and
      addressed issues of detection transparency

   o  Section 5 Addressed issue by recommending that users should be
      allowed to opt in to their desired method of notification

   o  Section 5.4 Addressed issue around timing of notification

   o  Section 5.4 Addressed Walled Garden issue by recommending that
      Walled Gardens are to be used as a notification method

   o  Section 5.7 Noted that there are alternative methods to that
      outlined in RFC6108

   o  Section 5.7 Noted that web notification is only intended for
      devices running a web browser

   o  Section 5.9 Fixed typo

   o  Section 6.1 Noted that ISPs should be clear when offering paid
      remediation services that these are aimed at those without skills
      to remediate or lacking confidence to do so

   o  Section 7 Noted that refusal to remediate is a business issue and
      not subject to technical recommendation.

   o  ALL open issues are now closed!

   -12 version:



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   o  Shortened reference names (non-RFC references)

   o  Closed Open Issue #1 and #4, as leaky walled gardens are covered
      in Section 5.4

   o  Closed Open Issue #2 and #6, by adding a section on users that
      fail to mitigate, including account termination

   o  Closed Open Issue #3, by adding a Privacy Considerations section
      to address PII

   o  Closed Open Issue #5, with no action taken

   o  Closed Open Issue #7, by leaving as Informational (the IETF can
      assess this later)

   o  Closed Open Issue #8, by generalizing the guided remediation
      section via the removal of specific links, etc.

   o  Closed Open Issue #9, by reviewing and updating remediation steps

   o  Changed some 'must' statements to 'should' statements (even though
      there is not RFC 2119 language in the document)

   o  ALL open issues are now closed!

   -11 version:

   o  Added reference to RFC 6108

   o  Per Sean Turner, removed RFC 2119 reference and section

   o  Per Donald Smith, externalized the reference to 3rd party data
      sources, now Appendix A

   o  Per Donald Smith, moved basic notification challenges into a new
      section at the end of the Notifications section.

   -10 version:

   o  Minor refresh to keep doc from expiring.  Several large updates
      planned in a Dec/Jan revision

   -09 version:

   o  Corrected nits pointed out by Sean





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   o  Removed occurrences of double spacing

   o  Grammar and spelling corrections in many sections

   o  Added text for leaky walled garden

   -08 version:

   o  Corrected a reference error in Section 10.

   o  Added a new informative reference

   o  Change to Section 5.a., to note additional port scanning
      limitations

   o  Per Joel Jaeggli, change computer to host, to conform to IETF
      document norms

   o  Several other changes suggested by Joel Jaeggli and Donald Smith
      on the OPSEC mailing list

   o  Incorp. other feedback received privately

   o  Because Jason is so very dedicated, he worked on this revision
      while on vacation ;-)

   -07 version:

   o  Corrected various spelling and grammatical errors, pointed out by
      additional reviewers.  Also added a section on information flowing
      from the user.  Lastly, updated the reviewer list to include all
      those who either were kind enough to review for us or who provided
      interesting, insightful, and/or helpful feedback.

   -06 version:

   o  Corrected an error in the version change log, and added some extra
      information on user remediation.  Also added an informational
      reference to BIOS infection.

   -05 version:

   o  Minor tweaks made by Jason - ready for wider review and next
      steps.  Also cleared open issues.  Lastly, added 2nd paragraph to
      security section and added sections on limitations relating to
      public and other shared network sites.  Added a new section on
      professional remediation.




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   -04 version:

   o  Updated reference to BIOS based malware, added wording on PII and
      local jurisdictions, added suggestion that industry body produce
      bot stats, added suggestion that ISPs use volunteer forums

   -03 version:

   o  all updates from Jason - now ready for wider external review

   -02 version:

   o  all updates from Jason - still some open issues but we're now at a
      place where we can solicit more external feedback

   -01 version:

   o  -01 version published


Appendix C.  Open Issues

   No open issues.


Authors' Addresses

   Jason Livingood
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: jason_livingood@cable.comcast.com
   URI:   http://www.comcast.com


   Nirmal Mody
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: nirmal_mody@cable.comcast.com
   URI:   http://www.comcast.com




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   Mike O'Reirdan
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: michael_oreirdan@cable.comcast.com
   URI:   http://www.comcast.com










































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