Tonight I finally figured out what was wrong with my notebook. The first symptom I notice was a general slowing of the system. And to my horror, Folder Options under Tools was gone. My antivirus acted strangely and my Spybot Search and Destroy refused to update itself.
Then I found a forum which described the symptoms so well. I had Brontok lurking inside my hard disk.
And after searching the net forums for a solution, I found one: Brontok Washer. Thank heavens it worked.
But now after such a scare, I'm backing up everything.