SpywareBlaster is a very good program, Also you can get spywaregaurd from javacool as well.
I run both on my system and they do a great job,
Can't forget about a firewall,
Here lets make it easy, grab a cup of coffee and have a read
Here
Make sure your current Anti Virus is updated, and run a free online scan as well just to double check things,
I didn't see Bitdefender listed as a free online scan, it's one of my favorites
bitdefender