Since this issue has come up an inordiante amount of times for me recently, I thought I would share some solid tips, tricks, and tools for keeping your PC safe, clean, and happy.
Get and run Spybot-Search and Destroy. Free to download and easy to use.
Get and Run AdAware. Free to download and easy to use.
Browse with Firefox instead of IE. Free to download and easy to use.
Run a free online "Panda-Scan" for viruses.
Panda Scan Link
Recommended add-ons for Firefox: