....chances are your scan isn't customized to detect all locations where spyware could be "hiding"
The standard smart scan only detects locations on your hard drive where spyware is most likely to be located.
However, if your do a customized scan, then Ad-Aware will search EVERY single file on your hard drive for spyware.
Oh, since decadence decided to beat me to the punch, I'll just end my post with a "Yeah, that!"
Thanks, decadence.
ETA: The customization of the Ad-Aware scan detected
414 spyware files on my computer, half of which were browser hijackers.
Ad-Aware is a VERY good anti-spyware tool, but you have to tweak it for maximum usefulness. Ditto for Spybot-Search and Destroy.
Threaded Mode