You might, and not even know it.

Who knows where it comes from? All those cookies, tracking programs, viruses, pop-up messages that seem to come from nowhere...

Especially on a shared computer, in a family environment or college dorm room, the crap just multiplies like bunnies in springtime.

Fortunately, there are some good, FREE ways to deal with it. The one I have been happiest with is Spybot Search and Destroy, which is free software from PepiMK Software.

A quick, free download, Spybot S&D will protect your system from spyware, trojan horses that can grant control of your computer to unknown scammers and spammers on the internet, keyloggers that can watch your computer activity and foward passwords and PIN numbers for credit cards and banking services to hackers, dialers that take over your modem to dial expensive 900 services or offshore telephone numbers (a particularly pernicious scam), etc.

It's well worth the quick download and installation.