The idea of someone hacking into my system in order to perpetrate a crime just makes me cringe.

There's a lot of good freeware available at download.com

I personally use:
-HijackThis
-Spybot Search and Destroy
-AdAware
-Spyware Blaster
-WinPatrol

Note: I'm in the IT biz. Be careful with some of these, particularly HijackThis and Spybot S&D (in advanced mode). If you aren't particularly computer savvy, leave HijackThis off your download list, and use Spybot in it's default mode only.