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What is a Trojan?

A Trojan Horse is a particular category of spyware. A Trojan is a program that infects your computer and allows a hacker to take control of your machine behind your back. A Trojan infection can allow total remote access to your computer by a third party.

Unlike virus and worms, Trojans do not replicate themselves so to get infected you must, one way or another, have downloaded the program onto your computer. This most commonly occurs when you download a program that pretends to be one thing while it is actually another. Hence the origin of the "Trojan" name.

The most common types of Trojans include such functions as the ability to steal all passwords cached or not (this is done using key logging technology), run files, do serious damage to your machine and do pretty much whatever the intruder wants.

However these days most Trojans are being used to turn your computer into a Zombie. In other words the hacker will be able to use your computer and a bunch of other infected computers like yours and turn them into an army of zombies to attack a more important target. This way the intruder can hide his or her own trace and use your computer as a front. This means the victim's firewall will show your Internet address in the log as the attacker's address and you may end up with several complaint letters to your ISP and even lose your account as a result.

So just because you think you have nothing important on your computer doesn't mean your computer itself and your bandwidth is not valuable to hackers. In fact they are quite valuable and worth the hacker's time.