(Coined By MIT-hacker-turned-NSA-spook Dan Edwards) A malicious, security-Breaking program that is disguised as something Benign, such as a directory lister, archiver, game, or (in one notorious 1990 case on the Mac) a program to find and destroy viruses! A Trojan horse is similar to a Back door. See also RFC 1135, worm, phage, mockingBird. [Jargon File] (1995-03-21)