1. A malicious computer program that may replicate itself on in a computer network, insert or attach copies of itself into computer programs, and cause harm to computers or systems by corrupting, stealing or modifying data or access. Voting system components connected to a network risk malware infections, such as viruses.

Source: Information Technology Terminology, U.S. Election Assistance Commission,

2. A computer program that can replicate itself, infect a computer without permission or knowledge of the user, and then spread or propagate to another computer.

Source: Explore Terms: A Glossary of Common Cybersecurity Terminology, National Initiative for Cybersecurity Careers and Studies (NICCS),

3. A software program, script, or macro that has been designed to infect, destroy, modify, or cause other problems with a computer or software program. (US Army TRADOC DCSINT Handbook 1.02, 15 Aug 2007).

4. A computer program that can copy itself and infect a computer without permission or knowledge of the user. (Wikipedia, accessed 2 Oct 2007). Malicious software; a form of Trojan horse that reproduces itself in other executable code. (DoD 5220.22.22-M-Sup 1, NISPOM Supplement, Feb 1995).

Source: Terms & Definitions of Interest for DoD Counterintelligence Professionals, Office of the National Counterintelligence,