What is a Trojan?

A Trojan is a program that may appear to be legitimate, but in fact does something malicious. Trojans are often used to gain backdoor access - that is to say remote, surreptitious access, to a user's system. Trojans do not replicate as viruses do, nor make copies of themselves as worms do. These are sometimes referred to as Remote Access Trojans, or RATs. >> More on Trojans