PCinfospace

Definition: http://en.wikipedia.org/wiki/Trojan_horse_(computing)  

This is not a virus you want on your computer.  It can be written to do almost anything.  It can even help spread other viruses.

PREVENTION> You must have the best Anti-Virus program you can find.  I am not in the business of promoting one or the other.  However I do not recommend the free ones. See: http://www.download.com/Antivirus-Firewall-Spyware/?tag=dir 
Viruses, spy-ware etc are way too aggressive to play games with.   Nobody wants to spend money on prevention.  Yet it would cost you a lot of money to have a professional to remove the infection.  In some cases these “enemies” WILL destroy your hard drive.