Right so my computer seems to be infected with some viruses.. I'm pretty sure this is the result of watching Heroes on some dubious site but anyway.. I got a free Symantec anti-virus thing from my university and am doing a full system scan for the second time right now. The first one doesn't seem to have fixed the problem since I still get random pop-ups, security alerts, and it takes forever for my computer to restart. So what can I do in addition to this?

Also I'm constantly getting "system alerts", it's this little exclamation point icon that keeps popping up on my toolbar. It says "click this balloon to download important blah blah blah".. I can't tell if this is something legitimate or just another virus.