Yes, it's a scam. Check this page about AdwareSheriff, from Network Associates, ie McAfee -
http://vil.nai.com/vil/content/v_138377.htm - er, I mean McAfee posted the info, not that McAfee wrote AdwareSheriff
Also, maybe you might want to read the advice listed on this page...
http://forums.techguy.org/security/4...iff-1-0-a.html