Folks, for an idea of companies that "never know" they appear in affiliate sites, maybe you could have a look at this post from Mark Russinovich:
http://www.sysinternals.com/blog/2006/01/antispyware-conspiracy.html
If you want to see how money flows, in case you don't know this link
http://www.benedelman.org/
I think you'll agree that things aren't that clear and vendors aren't that innocent... better purchase SW from very reputable companies. AV products now can do some scan for parasites, some firewalls have antispyware modules and specifically for malware that's not virus you have ad-aware, this Spybot and Ewido as credible companies, etc.
Don't buy the first thing you see in the net!
C.