virus

virus: 1. An unwanted program which places itself into other programs, which are shared among computer systems, and replicates itself. Note: A virus is usually manifested by a destructive or disruptive effect on the executable program that it affects. 2. Self-replicating, malicious program segment that attaches itself to an application program or other executable system component and leaves no obvious signs of its presence. [INFOSEC-99]