CERT Advisory - Keystroke Logging Banner

CERT Advisory cert-advisory-request at cert.org
Mon Dec 7 19:16:56 UTC 1992

CA-92:19                         CERT Advisory
                                December 7, 1992
                            Keystroke Logging Banner


The CERT Coordination Center has received information from the United States
Department of Justice, General Litigation and Legal Advice Section, Criminal
Division, regarding keystroke monitoring by computer systems administrators,
as a method of protecting computer systems from unauthorized access.

The information that follows is based on the Justice Department's advice
to all federal agencies.  CERT strongly suggests adding a notice banner
such as the one included below to all systems.  Sites not covered by U.S.
law should consult their legal counsel.


    The legality of such monitoring is governed by 18 U.S.C. section 2510
    et seq.  That statute was last amended in 1986, years before the words
    "virus" and "worm" became part of our everyday vocabulary.  Therefore,
    not surprisingly, the statute does not directly address the propriety
    of keystroke monitoring by system administrators.

    Attorneys for the Department have engaged in a review of the statute
    and its legislative history.  We believe that such keystroke monitoring
    of intruders may be defensible under the statute.  However, the statute
    does not expressly authorize such monitoring.  Moreover, no court has
    yet had an opportunity to rule on this issue.  If the courts were to
    decide that such monitoring is improper, it would potentially give rise
    to both criminal and civil liability for system administrators.
    Therefore, absent clear guidance from the courts, we believe it is
    advisable for system administrators who will be engaged in such
    monitoring to give notice to those who would be subject to monitoring
    that, by using the system, they are expressly consenting to such
    monitoring.  Since it is important that unauthorized intruders be given
    notice, some form of banner notice at the time of signing on to the
    system is required.  Simply providing written notice in advance to only
    authorized users will not be sufficient to place outside hackers on

    An agency's banner should give clear and unequivocal notice to
    intruders that by signing onto the system they are expressly consenting
    to such monitoring.  The banner should also indicate to authorized
    users that they may be monitored during the effort to monitor the
    intruder (e.g., if a hacker is downloading a user's file, keystroke
    monitoring will intercept both the hacker's download command and the
    authorized user's file).  We also understand that system administrators
    may in some cases monitor authorized users in the course of routine
    system maintenance.  If this is the case, the banner should indicate
    this fact.  An example of an appropriate banner might be as follows:

       This system is for the use of authorized users only.
       Individuals using this computer system without authority, or in
       excess of their authority, are subject to having all of their
       activities on this system monitored and recorded by system

       In the course of monitoring individuals improperly using this
       system, or in the course of system maintenance, the activities
       of authorized users may also be monitored.

       Anyone using this system expressly consents to such monitoring
       and is advised that if such monitoring reveals possible
       evidence of criminal activity, system personnel may provide the
       evidence of such monitoring to law enforcement officials.

Each site using this suggested banner should tailor it to their precise
needs.  Any questions should be directed to your organization's legal

The CERT Coordination Center wishes to thank Robert S. Mueller, III,
Scott Charney and Marty Stansell-Gamm from the United States Department
of Justice for their help in preparing this Advisory.

If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in FIRST (Forum of Incident
Response and Security Teams).

Internet E-mail: cert at cert.org
Telephone: 412-268-7090 (24-hour hotline)
           CERT personnel answer 7:30 a.m.-6:00 p.m. EST(GMT-5)/EDT(GMT-4),
           on call for emergencies during other hours.

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

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