This is from Lavasoft and I use it every day. The free version check for all the nasty adware, spyware, etc. I paid to have the plus version and that block stuff in realtime though it's pretty picky and I have to unload it to see pop ups on sites I trust. If you're not using this, you need to: make sure to check for updates every few days http://www.lavasoftusa.com/software/adaware/
AdAware is good stuff (paid for full ver). I also have AVG (paid for the full ver) , Spyware Begone (free) Spybot (free) and HiJack This (free) None of these are completely foolproof, my main machine is ill right now with some sort of OS glitch that arrived immediately after the move. (Never again will I let the box go with the movers.) I have to admit that the difficulty may not be related to something creeping in off the web, it could be a physical disruption from poor handling by the movers.
You might check out Microsoft's Beta version antispyware software. I use it at home and at work and it works really good. I use Adaware also, but the more you have the better you'll be.