I agree with Cache22, the programs used to fight the malware have been outpaced. That is why most forums and experts advise that a combination of tools is necessary to stay clean. I run a suite of tools to check for spyware/adware/malware, trojan horses and worms. It would be great if an "Anti-Parasite" suite is created saving me the effort of running upwards of 11 programs to keep my PC safe.
As for free anti-virus (or other free software for that matter) not being worth their purchase price I have these thoughts:
Spyware S&D and Ad-Aware are the most highly regarded Anti-Spy programs on the market. . . they're free!
Google Toolbar - Best pop-up blocker I've ever used . . . it's free
Avast! cleaned up 5 viruses on my computer and a combination of 16 viruses and trojans on a PC I worked on. Both PC's were protected by the burdening NAV with the heuristics set to their highest level of protection, automatic updates on and running, and active scanning set to deep scan. And Avast! (and it's AWESOME boot time scanner) . . . are free!
I'm new to the forums but not to PCs. I use a combination of pay and free tools to keep my PC clean. The greater good is to work towards an UBER TOOL that cleans temp files, temp internet files, cache, internet tracks, all forms of usage tracks (with plugins for 3rd party programs), top of class anti-virus, anti-spyware, anti-trojan, anti-worm, an excellent suite of system tools and . . .
Well the list goes on and on. Perhaps that's why no such tool exists. But an Anti-Parasite (anti-spy, anti-virus, anti-trojan, anti-worm) tool would be a good start!
Don't give up on the Freebies! Pay or Free amass an army of tools. The good guys are losing the battle.
Po