frostbite:
You might want to consider using Spybot a bit more; there's at least one update per week. After an update, you can 'Immunize' your PC against threats. Scanning is best done when you don't need the PC for half an hour or so.
Spybot has found a few bad items, over 3 years of use.
AdAware: still using AdAware Personal SE, not 2007. '07 version has been crtitcised as bloatware which is resource-hungry. Definitions updates for SE are available from
www.majorgeeks.com ; unzip the file to C\Program Files\Lavasoft\Ad-Aware SE Personal.
I don't recall AdAware ever finding anything nasty; just good for peace of mind.
Also use: SpywareBlaster and SpywareGuard.
Avast Home is the resident protection.