A Trojan virus works by obtaining unauthorized access to a computer's hard drive with the intent of causing loss or theft of data. Once the virus infects a computer it can block access to programs or information, copy data or even cause a disruption in performance.
There are many different types of Trojan viruses, and they are classified by the function they perform on a computer. A backdoor Trojan virus provides a backdoor access on a computer to an authorized user. Once inside the backdoor, the author of the virus is free to do anything to the infected computer including rebooting the computer, wiping the computer free from data and sending malicious files to others.
A Trojan banker virus steals personal banking information with the intent of defrauding the user. This may also include stealing credit card numbers.
There are also Trojan game thief viruses developed by online gamers who gain access to other players with the intent of stealing credentials, game currency and personal information. These online gamers may also use stored account information to pay for their own gaming memberships, which can sometimes result in excessive monetary losses to the victim. This type of virus can affect computers and even gaming systems that access online play with other users.