I politely ask them to leave.
Well, I fixed the virus problem. And it only took THE ENTIRE FRIGGEN DAY. Lost all my data for A Knight's Story as collateral damage. It's an idle game where you just watch your knight hack and slash monsters and grow in levels. Good way to progress in a game without wasting time. Just check up on the little dude every so often. Three straight weeks of "playing" it and he's back to level 1. Tristan the Hero is now Tristan the Noob.
...damn, all my saved data at Kongregate is gone. That reeeallly sucks.