(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)