There are many people who have suffered from acquiring a Trojan horse on their computer.  This virus was named after the infamous mythological wooden horse that was left outside of the city of Troy during the Trojan War.  Inside this wheeled structure were hidden many soldiers who attacked the city after they fell asleep.  Just like the wooden horse, a Trojan virus can come disguised in a pretty package.

This kind of virus is actually not something new.  Many people saying that they have come around only in the past six to eight years when in actuality they were actually thought up way back in 1983.  Although personal computing was not really introduced until much later, it was discussed that a virus could actually be hidden in the form of malicious code as a UNIX login.  This actually came true in the form of the Trojan virus that we are familiar with today.

There are many different types of viruses that can infect your computer.  Some of them travel from server to server, and from computer to computer infecting you without you doing anything at all.  They are self replicating and attach themselves to many different files in order to do whatever they were programmed to do.  Most times this type of virus will either send personal information from your computer to someone else or they may all attack a certain server in order to deny its service.  This is what is known as a denial of service attack.

The Trojan horse is different in that it is hidden inside a file that looks innocent.  These files may be sent to you through an email or perhaps you may download something and the virus is hidden inside of it.  The good news is, it cannot install on its own.  It relies on you to initiate the install by running the program where it is hidden.  Once on your computer, they can do a number of different things.  Some of the more harmful things that they can do are to completely take over your computer and lock you out, run a key-logger script that can steal passwords and even credit card information, or destroy various data that is on your hard drive rendering it inoperable.

Another thing that this kind of virus can do is to open the ports on your computer and allow other spyware programs and malware to be installed.  This can create an almost never ending cycle of virus installs that is very hard to get ahead of.  Sometimes it is necessary to get professional help in order to clean a heavily infected computer.

Just as the original Greek wooden horse looked good on the outside but contained something bad on the inside, a Trojan virus is also hidden inside of something that looks good on the outside.  So always be careful of anything that you run, and if you are unsure of where it came from then don't run it at all.