Note
My other home PC, the old one, had a trojan virus. I disablde firewall some time ago and I forgot to put it back. I think I managed to kill it, but I also followed some wrong instructons from the web and deleted some files I shouldn't have, and finally PC did not work much at all. Tried to re-install OS (win98...), but something went wrong after copying files - it didn't reboot as it should during the install session. So it tried to repair it by restoring old cofiguration. And now all working again, no re-instal made, no viruses found so far - it's still scanning. I think I was lucky. Or I hope - it's still scanning....
One of my co-workers managed to get trojan just by being connected to web for one hour without any protection. ISP change, previous had firewall, new had not...