A Trojan (abbreviated as Trojan) is a malicious computer program that can copy itself and can steal user information without the user's knowledge. It is one of the three main types of malware: worms, viruses and Trojans. The Trojan horse earned this type of malware its name from Greek mythology, in which a wooden horse was used as a ruse to destroy the city of Troy. In fact, the first computer Trojans originally pretended to be useful programs, and many of them still look like that today.
Trojan horses can be just as harmful as traditional computer viruses, and can often pose as a program to help remove spyware or Trojans while introducing them into the computer itself.
Hackers can use a Trojan horse to gain remote control of a computer and is limited only by the user privileges set and the design of the Trojan in question. A hacker who gains control of a computer in this way can then use it as:
- botnet
- steal data and information from it
- install other malware
- edit or delete files
- monitor keystroke logging
- monitor the user's screen and behaviour on the Internet and on the computer
- crash the system
