RFC3067: TERENA'S Incident Object Description and Exchange Format Requirements

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Network Working Group                                       J. Arvidsson
Request for Comments: 3067                                    Telia CERT
Category: Informational                                       A. Cormack
                                                            Y. Demchenko
                                                               J. Meijer
                                                           February 2001

 TERENA's Incident Object Description and Exchange Format Requirements

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.


   The purpose of the Incident Object Description and Exchange Format is
   to define a common data format for the description, archiving and
   exchange of information about incidents between CSIRTs (Computer
   Security Incident Response Teams) (including alert, incident in
   investigation, archiving, statistics, reporting, etc.).  This
   document describes the high-level requirements for such a description
   and exchange format, including the reasons for those requirements.
   Examples are used to illustrate the requirements where necessary.

1. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

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2. Introduction

   This document defines requirements for the Incident object
   Description and Exchange Format (IODEF), which is the intended
   product of the Incident Taxonomy Working Group (ITDWG) at TERENA [2].
   IODEF is planned to be a standard format which allows CSIRTs to
   exchange operational and statistical information; it may also provide
   a basis for the development of compatible and inter-operable tools
   for Incident recording, tracking and exchange.

   Another aim is to extend the work of IETF IDWG (currently focused on
   Intrusion Detection exchange format and communication protocol) to
   the description of incidents as higher level elements in Network
   Security.  This will involve CSIRTs and their constituency related

   The IODEF set of documents of which this document is the first will
   contain IODEF Data Model and XML DTD specification.  Further
   discussion of this document will take place in the ITDWG mailing
   lists <incident-taxonomy@terena.nl> or <iodef@terena.nl>, archives
   are available correspondently at
   http://hypermail.terena.nl/incident-taxonomy-list/mail-archive/ and

2.1. Rationale

   This work is based on attempts to establish cooperation and
   information exchange between leading/advanced CSIRTs in Europe and
   among the FIRST community.  These CSIRTs understand the advantages of
   information exchange and cooperation in processing, tracking and
   investigating security incidents.

   Computer Incidents are becoming distributed and International and
   involve many CSIRTs across borders, languages and cultures.  Post-
   Incident information and statistics exchange is important for future
   Incident prevention and Internet security improvement.  The key
   element for information exchange in all these cases is a common
   format for Incident (Object) description.

   It is probable that in further development or implementation the
   IODEF might be used for forensic purposes, and this means that
   Incident description must be unambiguous and allow for future custody
   (archiving/documentation) features.

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   Another issue that is targeted by developing IODEF is a need to have
   higher level Incident description and exchange format than will be
   provided by IDS (Intrusion Detection Systems) and the proposed IDEF
   (Intrusion Detection Exchange Format).  Compatibility with IDEF and
   other related standards will be satisfied by the IODEF requirement on
   modularity and extensibility.  IODEF should vertically be compatible
   with IDMEF, IODEF might be able to include or reference IDMEF Alert
   message as initial information about Incident.

2.2. Incident Description Terms

   A definition of the main terms used in the rest of document is given
   for clarity.

   Where possible, existing definitions will be used; some definitions
   will need additional detail and further consideration.

   Taxonomy of the Computer Security Incident related terminology made
   by TERENA's ITDWG [2] is presented in [12].

2.2.1. Attack

   An assault on system security that derives from an intelligent
   threat, i.e., an intelligent act that is a deliberate attempt
   (especially in the sense of a method or technique) to evade security
   services and violate the security policy of a system.

   Attack can be active or passive, by insider or by outsider, or via
   attack mediator.

2.2.2. Attacker

   Attacker is individual who attempts one or more attacks in order to
   achieve an objective(s).

   For the purpose of IODEF attacker is described by its network ID,
   organisation which network/computer attack was originated and
   physical location information (optional).

2.2.3. CSIRT

   CSIRT (Computer Security Incident Response Team) is used in IODEF to
   refer to the authority handling the Incident and creating Incident
   Object Description.  The CSIRT is also likely to be involved in
   evidence collection and custody, incident remedy, etc.

   In IODEF CSIRT represented by its ID, constituency, public key, etc.

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2.2.4. Damage

   An intended or unintended consequence of an attack which affects the
   normal operation of the targeted system or service.  Description of
   damage may include free text description of actual result of attack,
   and, where possible, structured information about the particular
   damaged system, subsystem or service.

2.2.5. Event

   An action directed at a target which is intended to result in a
   change of state (status) of the target.  From the point of view of
   event origination, it can be defined as any observable occurrence in
   a system or network which resulted in an alert being generated.  For
   example, three failed logins in 10 seconds might indicate a brute-
   force login attack.

2.2.6. Evidence

   Evidence is information relating to an event that proves or supports
   a conclusion about the event. With respect to security incidents (the
   events), it may include but is not limited to: data dump created by
   Intrusion Detection System (IDS), data from syslog file, kernel
   statistics, cache, memory, temporary file system, or other data that
   caused the alert or were collected after the incident happened.

   Special rules and care must be taken when storing and archiving
   evidence, particularly to preserve its integrity.  When necessary
   evidence should be stored encrypted.

   According to the Guidelines for Evidence Collection and Archiving
   (Evidence) evidence must be strictly secured.  The chain of evidence
   custody needs to be clearly documented.

   It is essential that evidence should be collected, archived and
   preserved according to local legislation.

2.2.7. Incident

   An Incident is a security event that involves a security violation.
   An incident can be defined as a single attack or a group of attacks
   that can be distinguished from other attacks by the method of attack,
   identity of attackers, victims, sites, objectives or timing, etc.

   An incident is a root element of the IODEF. In the context of IODEF,
   the term Incident is used to mean a Computer Security Incident or an
   IT Security Incident.

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   However we should distinguish between the generic definition of
   'Incident' which is an event that might lead to damage or damage
   which is not too serious, and 'Security Incident' and 'IT Security
   Incident' which are defined below:

   a) Security incident is an event that involves a security violation.
      This may be an event that violates a security policy, UAP, laws
      and jurisdictions, etc. A security incident may also be an
      incident that has been escalated to a security incident.

      A security incident is worse than an incident as it affects the
      security of or in the organisation. A security incident may be
      logical, physical or organisational, for example a computer
      intrusion, loss of secrecy, information theft, fire or an alarm
      that doesn't work properly.  A security incident may be caused on
      purpose or by accident.  The latter may be if somebody forgets to
      lock a door or forgets to activate an access list in a router.

   b) An IT security incident is defined according to [9] as any real or
      suspected adverse event in relation to the security of a computer
      or computer network.  Typical security incidents within the IT
      area are: a computer intrusion, a denial-of-service attack,
      information theft or data manipulation, etc.

2.2.8. Impact

   Impact describes result of attack expressed in terms of user
   community, for example the cost in terms of financial or other

2.2.9. Target

   A computer or network logical entity (account, process or data) or
   physical entity (component, computer, network or internetwork).

2.2.10. Victim

   Victim is individual or organisation which suffered the attack which
   is described in incident report.

   For the purpose of IODEF victim is described by its network ID,
   organisation and location information.

2.2.11. Vulnerability

   A flaw or weakness in a system's design, implementation, or operation
   and management that could be exploited to violate the system's
   security policy.

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   Most systems have vulnerabilities of some sort, but this does not
   mean that the systems are too flawed to use.  Not every threat
   results in an attack, and not every attack succeeds.  Success depends
   on the degree of vulnerability, the strength of attacks, and the
   effectiveness of any countermeasures in use.  If the attacks needed
   to exploit a vulnerability are very difficult to carry out, then the
   vulnerability may be tolerable.  If the perceived benefit to an
   attacker is small, then even an easily exploited vulnerability may be
   tolerable.  However, if the attacks are well understood and easily
   made, and if the vulnerable system is employed by a wide range of
   users, then it is likely that there will be enough benefit for
   someone to make an attack.

2.2.12. Other terms

   Other terms used: alert, activity, IDS, Security Policy, etc. - are
   defined in related I-Ds, RFCs and standards [3, 6, 7, 8, 9, 10].

3. General Requirements

3.1. The IODEF shall reference and use previously published RFCs
     where possible.

   The IETF has already developed a number of standards in the areas of
   networks and security that are actually deployed in present Internet.
   Current standards provide framework for compatibility of IODEF with
   other related technologies necessary to operate /implement IODEF in
   practice.  Another issue of compatibility for the IODEF is its
   general compatibility with IDEF currently being developed by IETF
   IDEWG.  In the interest of time and compatibility, defined and
   accepted standards should be used wherever possible.

   In particularly, IODEF specification proposals SHOULD rely heavily on
   existing communications, encryption and language standards, where

4. Description Format

4.1. IODEF shall support full internationalization and localization.

   Since some Incidents need involvement of CSIRTs from different
   countries, cultural and geographic regions, the IODEF description
   must be formatted such that they can be presented to an operator in a
   local language and adhering to local presentation formats.

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   Although metalanguage for IODEF identifiers and labels is considered
   to be English, a local IODEF implementation might be capable to
   translate metalanguage identifiers and labels into local language and
   presentations if necessary.

   Localized presentation of dates, time and names may also be required.
   In cases where the messages contain text strings and names that need
   characters other than Latin-1 (or ISO 8859-1), the information
   preferably should be represented using the ISO/IEC IS 10646-1
   character set and encoded using the UTF-8 transformation format, and
   optionally using local character sets and encodings [13].

4.2. The IODEF must support modularity in Incident description to
     allow aggregation and filtering of data.

   It is suggested that Incident description with IODEF might include
   external information, e.g., from IDS, or reference externally stored
   evidence custody data, or such information might be removed from
   current IODEF description, e.g., in purposes of privacy or security.
   Another practical/real life motivation for this requirement is to
   give possibility for some CSIRTs/managers to perform filtering and/or
   data aggregation functions on IODEF descriptions for the purposes of
   statistics, reporting and high level Incident information exchange
   between CSIRTs and/or their constituency and sponsors.

   Therefore the IODEF descriptions MUST be structured to facilitate
   these operations.  This also implies to strong IODEF semantics.

4.3. IODEF must support the application of an access restriction
     policy attribute to every element.

   IODEF Incident descriptions potentially contain sensitive or private
   information (such as passwords, persons/organisations identifiers or
   forensic information (evidence data)) and in some cases may be
   exposed to non-authorised persons.  Such situations may arise
   particularly in case of Incident information exchange between CSIRTs
   or other involved bodies.  Some cases may be addressed by encrypting
   IODEF elements, however this will not always be possible.

   Therefore, to prevent accidental disclosure of sensitive data, parts
   of the IODEF object must be marked with access restriction
   attributes.  These markings will be particularly useful when used
   with automated processing systems.

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5. Communications Mechanisms Requirements

5.1. IODEF exchange will normally be initiated by humans using
     standard communication protocols, for example, e-mail, WWW/HTTP,

   IODEF description is normally created by a human using special or
   standard text editors.  The IODEF is targeted to be processed by
   automated Incident handling systems but still must be human readable,
   able to be viewed and browsed with standard tools (e.g., browsers or
   electronic table processors or database tools like MS Excel or
   Access).  Incident information exchange will normally require
   authorisation by  an operator or CSIRT manager so is not expected to
   be initiated automatically.  The role of Incident handling system is
   to provide assistance and tools for performing the exchange.

   It is important to distinguish the purposes of the machine readable
   and exchangeable IDEF Intrusion message format and the human oriented
   and created IODEF Incident description.

   Communications security requirements will be applied separately
   according to local policy so are not defined by this document.

6. Message Contents

6.1. The root element of the IO description should contain a unique
     identification number (or identifier), IO purpose and default
     permission level

   Unique identification number (or identifier) is necessary to
   distinguish one Incident from another.  It is suggested that unique
   identification number will contain information at least about IO
   creator, i.e. CSIRT or related body.  The classification of the
   Incident may also be used to form a unique identification number.  IO
   purpose will actually control which elements are included in the
   IODEF object Purposes may include incident alert/registration,
   handling, archiving, reporting or statistics.  The purpose, incident
   type or status of Incident investigation may require different levels
   of access permission for the Incident information.

   It is considered that root element of the IODEF will be <INCIDENT>
   and additional information will be treated as attributes of the root

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6.2. The content of the IODEF description should contain the type of
     the attack if it is known.

   It is expected that this type will be drawn from a standardized list
   of events; a new type of event may use a temporary implementation-
   specific type if the event type has not yet been standardized.

   Incident handling may involve many different staff members and teams.
   It is therefore essential that common terms are used to describe

   If the event type has not yet been standardized, temporary type
   definition might be given by team created IO.  It is expected that
   new type name will be self-explanatory and derived from a similar,
   existing type definition.

6.3. The IODEF description must be structured such that any relevant
     advisories, such as those from CERT/CC, CVE, can be referenced.

   Using standard Advisories and lists of known Attacks and
   Vulnerabilities will allow the use of their recommendations on
   Incident handling/prevention.  Such information might be included as
   an attribute to the attack or vulnerability type definition.

6.4. IODEF may include a detailed description of the attack that
     caused the current Incident.

   Description of attack includes information about attacker and victim,
   the appearance of the attack and possible impact.  At the early stage
   of Intrusion alert and Incident handling there is likely to be
   minimal information, during handling of the Incident this will grow
   to be sufficient for Incident investigation and remedy. Element
   <ATTACK> should be one of the main elements of Incident description.

6.5. The IODEF description must include or be able to reference
     additional detailed data related to this specific underlying
     event(s)/activity, often referred as evidence.

   For many purposes Incident description does not need many details on
   specific event(s)/activity that caused the Incident; this information
   may be referenced as external information (by means of URL).  In some
   cases it might be convenient to store separately evidence that has
   different access permissions.  It is foreseen that another standard
   will be proposed for evidence custody [5].

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6.6. The IODEF description MUST contain the description of the
     attacker and victim.

   This information is necessary to identify the source and target of
   the attack.  The minimum information about attacker and victim is
   their IP or Internet addresses, extended information will identify
   their organisations allowing CSIRTs to take appropriate measures for
   their particular constituency.

6.7. The IODEF description must support the representation of
     different types of device addresses, e.g., IP address (version 4 or
     6) and Internet name.

   The sites from which attack is launched might have addresses in
   various levels of the network protocol hierarchy (e.g., Data layer 2
   MAC addresses or Network layer 3 IP addresses).  Additionally, the
   devices involved in an intrusion event might use addresses that are
   not IP-centric, e.g., ATM-addresses.  It is also understood that
   information about the source and target of the attack might be
   obtained from IDS and include the IP address, MAC address or both.

6.8. IODEF must include the Identity of the creator of the Incident
     Object (CSIRT or other authority).  This may be the sender in an
     information exchange or the team currently handling the incident.

   The identity of Incident description creator is often valuable
   information for Incident response.  In one possible scenario the
   attack may progress through the network, comparison of corresponding
   incidents reported by different authorities might provide some
   additional information about the origin of the attack.  This is also
   useful information at post-incident information handling/exchange

6.9. The IODEF description must contain an indication of the
     possible impact of this event on the target.  The value of this
     field should be drawn from a standardized list of values if the
     attack is recognized as known, or expressed in a free language by
     responsible CSIRT team member.

   Information concerning the possible impact of the event on the target
   system provides an indication of what the attacker is attempting to
   do and is critical data for the CSIRTs to take actions and perform

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   damage assessment.  If no reference information (Advisories) is
   available, this field may be filled in based on CSIRT team

   It is expected that most CSIRTs will develop Incident handling
   support systems, based on existing Advisories (such as those from
   CERT/CC, CVE, etc.) that usually contain list of possible impacts for
   identified attacks.

   This also relates to the development of IDEF which will be
   implemented in intelligent IDS, able to retrieve information from
   standard databases of attacks and vulnerabilities [3].

6.10. The IODEF must be able to state the degree of confidence in
      the report information.

   Including this information is essential at the stage of Incident
   creation, particularly in cases when intelligent automatic IDS or
   expert systems are used.  These normally use statistical engines to
   estimate the event probability.

6.11. The IODEF description must provide information about the
      actions taken in the course of this incident by previous CSIRTs.

   The IODEF describes an Incident throughout its life-time from Alert
   to closing and archiving.  It is essential to track all actions taken
   by all involved parties.  This will help determine what further
   action needs to be taken, if any.  This is especially important in
   case of Incident information exchange between CSIRTs in process of

6.12. The IODEF must support reporting of the time of all stages
      along Incident life-time.

   Time is important from both a reporting and correlation point of
   view.  Time is one of main components that can identify the same
   Incident or attack if launched from many sites or distributed over
   the network.  Time is also essential to be able to track the life of
   an Incident including Incident exchange between CSIRTs in process of

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6.13. Time shall be reported as the local time and time zone offset
      from UTC.  (Note: See RFC 1902 for guidelines on reporting time.)

   For event correlation purposes, it is important that the manager be
   able to normalize the time information reported in the IODEF

6.14. The format for reporting the date must be compliant with all
      current standards for Year 2000 rollover, and it must have
      sufficient capability to continue reporting date values past the
      year 2038.

   It is stated in the purposes of the IODEF that the IODEF shall
   describe the Incident throughout its life-time.  In the case of
   archiving this duration might be unlimited.  Therefore,
   implementations that limit expression of time value (such as 2038
   date representation limitation in "Unix time") MUST be avoided.

6.15. Time granularity in IO time parameters shall not be specified
      by the IODEF.

   The time data may be included into IODEF description by existing
   information systems, retrieved from incident reporting messages or
   taken from IDS data or other event registration tools.  Each of these
   cases may have its own different time granularity.  For the purposes
   of implementation, it should be possible to handle time at different
   stages according to the local system capabilities.

6.16. The IODEF should support confidentiality of the description

   The selected design should be capable of supporting a variety of
   encryption algorithms and must be adaptable to a wide variety of

   IODEF Incident descriptions potentially contain sensitive or private
   information (such as forensic data (evidence data), passwords, or
   persons/organisations identifiers) which would be of great interest
   to an attacker or malefactor.  Incident information normally will be
   stored on a networked computer, which potentially may be exposed to
   attacks (or compromised).  Incident information may be transmitted
   across uncontrolled network segments.  Therefore, it is important
   that the content be protected from unauthorised access and
   modification.  Furthermore, since the legal environment for privacy

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   and encryption technologies are varied from regions and countries and
   change often, it is important that the design selected be capable of
   supporting a number of different encryption options and be adaptable
   by the user to a variety of environments. Additional measures may be
   undertaken for securing the Incident during communication but this
   issue is outside of IODEF scope as it implies more strict rules for
   IO archiving and storing in general.

6.17. The IODEF should ensure the integrity of the description

   The selected design should be capable of supporting a variety of
   integrity mechanisms and must be adaptable to a wide variety of

   Special measures should be undertaken to prevent malicious IO

   Additional measures may be undertaken for securing the Incident
   during communication but this issue is outside of IODEF scope.

6.18. The IODEF should ensure the authenticity and non-repudiation
      of the message content.

   Authenticity and accountability is needed by many teams, especially
   given the desire to automatically handle IOs, therefore it MUST be
   included in the IODEF.  Because of the importance of IO authenticity
   and non-repudiation to many teams and especially in case of
   communication between them, the implementation of these requirements
   is strongly RECOMMENDED.

6.19. The IODEF description must support an extension mechanism
      which may be used by implementers.  This allows future
      implementation-specific or experimental data.  The implementer
      MUST indicate how to interpret any included extensions.

   Implementers might wish to supply extra data such as information for
   internal purposes or necessary for the particular implementation of
   their Incident handling system.  These data may be removed or not in
   external communications but it is essential to mark them as
   additional to prevent wrong interpretation by different systems.

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6.20. The semantics of the IODEF description must be well defined.

   IODEF is a human oriented format for Incident description, and IODEF
   description should be capable of being read by humans.  The use of
   automatic parsing tools is foreseen but should not be critically
   necessary.  Therefore, IODEF must provide  good semantics, which will
   be  key to understanding what the description contains.  In some
   cases the IODEF description will be used for  automatic decision
   making, so it is important that the description be interpreted
   correctly.  This is an argument for using language-based semantics.
   The metalanguage for IODEF identifiers and labels is proposed to be
   English, a local IODEF implementation might be able to translate
   metalanguage identifiers and labels into local language and
   presentations if necessary.

7. IODEF extensibility

7.1. The IODEF itself MUST be extensible.  It is essential that when
     the use of new technologies and development of automated Incident
     handling system demands extension of IODEF, the IODEF will be
     capable to include new information.

   In addition to the need to extend IODEF to support new Incident
   handling tools, it is also suggested that IODEF will incorporate new
   developments from related standardisation areas such as IDEF for IDS
   or the development of special format for evidence custody.  The
   procedure for extension should be based on CSIRT/IODEF community

8. Security Considerations

   This memo describes requirements to an Incident Object Description
   and Exchange Format, which intends to define a common data format for
   the description, archiving and exchange of information about
   incidents between CSIRTs (including alert, incident in investigation,
   archiving, statistics, reporting, etc.).  In that respect the
   implementation of the IODEF is a subject to security considerations.
   Particular security requirement to access restriction indication is
   discussed in section 4.3, requirements to Incident description
   confidentiality, integrity, authenticity and non-repudiation are
   described in sections 6.16, 6.17, 6.18.

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9. References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Incident Taxonomy and Description Working Group Charter -

   [3]  Intrusion Detection Exchange Format Requirements by Wood, M. -
        December 2000, Work in Progress.

   [4]  Intrusion Detection Message Exchange Format Extensible Markup
        Language (XML) Document Type Definition by D. Curry, H. Debar -
        February 2001, Work in Progress.

   [5]  Guidelines for Evidence Collection and Archiving by Dominique
        Brezinski, Tom Killalea - July 2000, Work in Progress.

   [6]  Brownlee, N. and E. Guttman, "Expectations for Computer Security
        Incident Response", BCP 21, RFC 2350, June 1998.

   [7]  Shirey, R., "Internet Security Glossary", FYI 36, RFC 2828, May

   [8]  Establishing a Computer Security Incident Response Capability
        (CSIRC). NIST Special Publication 800-3, November, 1991

   [9]  Handbook for Computer Security Incident Response Teams (CSIRTs),
        Moira J. West-Brown, Don Stikvoort, Klaus-Peter Kossakowski. -
        CMU/SEI-98-HB-001. - Pittsburgh, PA: Carnegie Mellon University,

   [10] A Common Language for Computer Security Incidents by John D.
        Howard and Thomas A. Longstaff. -  Sandia Report: SAND98-8667,
        Sandia National Laboratories -

   [11] Best Current Practice of incident classification and reporting
        schemes currently used by active CSIRTs. -

   [12] Taxonomy of the Computer Security Incident related terminology -

   [13] Multilingual Support in Internet/IT Applications. -

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   This document was discussed at the Incident Taxonomy and Description
   Working Group seminars (http://www.terena.nl/task-forces/tf-
   csirt/tf-csirt000929prg.html#itdwg) in the frame of TERENA Task Force
   TF-CSIRT (http://www.terena.nl/task-forces/tf-csirt/).  Incident
   Taxonomy and Description Working Group at TERENA can be contacted via
   the mailing lists <incident-taxonomy@terena.nl> or <iodef@terena.nl>,
   archives are available correspondently at
   http://hypermail.terena.nl/incident-taxonomy-list/mail-archive/ and

Authors' Addresses

   Jimmy Arvidsson
   Telia CERT

   EMail: Jimmy.J.Arvidsson@telia.se

   Andrew Cormack

   EMail: Andrew.Cormack@ukerna.ac.uk

   Yuri Demchenko

   EMail: demch@terena.nl

   Jan Meijer

   EMail: jan.meijer@surfnet.nl

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Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
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Arvidsson, et al.            Informational                     [Page 17]