The 11/20/2007 edition of PC Magazine tested PC Tools ThreatFire 3(TF3) behavior-based scanner. According to the article, it blocked installation of every category of malware except rogue antispyware. It beat out Symantec's Norton AntiBot and Webroot's Spy Sweeper. TF3 also had no false positives, a problem with behavior-based scanning. The article recommended the free version but stated the commercial Pro version failed at cleaning up infested systems.
I thought this was an antispyware utility but it's listed as an antivirus utility at their website. I checked the comparison between the Pro and Free versions and the Free version does not have the antivirus engine. Also, here's a twist. The Free version has a real-time scanner but you can't do on-demand scanning. It's usually the opposite for crippleware trial versions of antispyware utilities.
I'm going to download this tonight and will report back on how it installed and worked. Since it has to be on all the time to work, I'll be interested in the RAM that it uses.
For those interested, here is a link to the download page: