I'm not a hacker but I need to know if anyone knows of something that fits this description...

I met a guy that was at my house a few times and I let him use my computer. I cut ties w/ him and he's VERY bitter now, and my myspace profile and other profiles on other sites have somehow gotten deleted all of a sudden... this guy sent me messages and he knows several NEW websites I've gone to recently that i NEVER told him about.

Is there something he could have done to my computer when he was at my house so that he can see what pages I go to and get my passwords???

Please reply with any ideas!! Thank you