What is a trojan horse?
A Trojan horse, or simply Trojan, is malware masquerading as legitimate software, named after the famous Trojan horse in which ancient Greek soldiers smuggled themselves into Troy. Trojans often act as a backdoor to give an attacker remote access to a user’s computer. See also backdoor.
How does a trojan horse work?
Unlike viruses and worms, trojans generally do not spread themselves. Trojan’s are often spread through some sort of social engineering, such as phishing. See social engineering and phishing.
The purpose of a trojan can range from destroying the victim’s system to using their resources as part of a botnet, extorting money, and stealing data. Up-to-date antivirus software and vigilance on the part of the user are the best defenses against trojans.