Trojan: Any program with a hidden intent. Trojans are one of the leading causes of breaking into machines. If you pull down a program from a chat room, new group, or even from unsolicited e-mail, then the program is likely trojaned with some subversive purpose. The word Trojan can be used as a verb: To trojan a program is to add subversive functionality to an existing program. For example, a trojaned login program might be programmed to accept a certain password for any user’s account that the hacker can use to log back into the system at any time. Rootkits often contain a suite of such trojaned programs.