This is a form of malware that hides inside a legitimate program that you can download like games, movies, free antivirus programs. So be careful what you download because you might get something unwanted. Some of the big names in Trojans are Sub7, Beast, Vundo, Koobface, Zeus and many others. Zeus' goal was to steal banking information using keyloggers that record all keys entered and can easily find passwords and usernames. Zeus was also behind the information leak from the United States Department of Transportation. It also impacted NASA, Amazon, ABC, Bank of America, and many other major companies. The best way to combat this problem is to make sure your antivirus software is up and up to date. Anyway, AVG, Avast. Their definitions will be constantly updated to combat all newly created viruses. Lately things have changed, it's less about bragging rights and more about monetary gain. Some of the ways they do this is by creating a large network of bot computers that can be used for spam or a DDOS (distributed denial of service) attack. They use viruses that encrypt commercial databases and use DDOS attacks and demand a ransom to stop this. (Nash) Reason why I wrote a Trojan horse. They can give a hacker remote access to your system. May crash the computer with a blue screen of death. Reformat hard drive, date or money stolen. A scary case that has been in the news a lot lately is the access to the infected webcam and the ransom demand not to be made public. The effects of a Trojan are almost endless, you can hide anything you want with it