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  • CERT Advisory CA-1992-19 Keystroke Logging Banner

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Original issue date: December 7, 1992
Last revised: September 19, 1997
Attached copyright statement

A complete revision history is at the end of this file.

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 notice.

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 counsel.

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.

Copyright 1992 Carnegie Mellon University.

Revision History
September 19,1997  Attached copyright statement
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