Yea watching others that use your comp is great advice. I let my brother's friends use mine once way back in 1999 and ended up with a ton of p0rn pop-up's and programs installed (dialers to p0rn servers and such).
Took me forever to clean that mess up....and now I don't even allow my parents or anyone else for that matter to use my comp, unless I am in the room, hands on keyboard and mouse, letting them feed me intructions.
[high]* Brad pats comp
[/high]
She's my baby