[Fedora]

I don't wanna sound scary, but you may have bigger problems than just a virus. Do you have a hardware firewall of some kind on your internet connection?

Yes, I have Norton Internet Security which has a firewall. The firewall picked up two virus attacks shortly before my system locked up. One it said it deleted, the other it was unable to repair. Usually when that happens it's no big deal, so I didn't run the antivirus scan right away--was going to do it later--now I wish I would've run it.

[Ramius]

It might not be a virus. It might be someone exploiting an unpatched vulnerability in your system.

I'm a big fan of hardware firewalls. Software firewalls are still a good thing, but a good hardware device, like a Netgear ProSafe device... is indispensable. They'll cover you even if your system is vulnerable.