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Viruses and worms are pretty basic, they infect and they spread. Trojans on the other hand do not. But my question is, what do trojans really do? I guess that depends on the payload? Are they (the term trojan) basically just delivery systems for whatever malware they carry with them?

All elaborations are welcome.

marked as duplicate by WhiteWinterWolf, Matthew, Neil Smithline, schroeder Jun 18 '16 at 18:32

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  • Yes, Trojans typically just provide access, whether it's a persistent backdoor, or a one-time "dropper". Generally, there's a payload program that uses that access to actually do whatever malicious thing the attacker is getting access to do. – HopelessN00b Jun 13 '16 at 19:09

From Wikipedia:

Trojan horse, or Trojan, is any malicious computer program which is used to hack into a computer by misleading users of its true intent. The term is derived from the Ancient Greek story of the wooden horse that was used to help Greek troops invade the city of Troy by stealth.

Therefore the difference is that a trojan horse is supposedly an useful program, or a game, or anything else that the user would like to run; however, when it is run, it also executes harmful code such as stealing the user's CC number or implanting a rootkit for remote control of the victim's computer.

Viruses and worms, on the other hand, cannot exist by themselves; they live and replicate by attaching themselves to files (in the case of viruses) or using network communication protocols (worms).

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