Forum Moderators: open
But if you want to keep using Windows, check out download dot com and search for "trojan."
I'd be tempted to do a reformat and then load up on all the anti-trojan & anti-virus software, just in the case that you have something that they have trouble catching. And then be very careful afterwards.
This would log everything you type - usernames, passwords, credit card numbers, personal correspondence -- and then upload it elsewhere for somebody to use this information maliciously.
I think they can also turn your PC into a zombie, which would allow them to launch DDoS attacks. Especially a problem if you're on a high speed internet connection and you leave it on all the time.
It's really something you need to take care of, even if it is something less dangerous.