Do I or don't I have an infection?
Running Windows 7 32 bit, IE8, Avast 5.0, and current Malwarebytes. While trying to access a site I visit regularly Avast reported a threat from HTML:Iframe-inf and blocked access to the site. Both a Quick scan and a Full scan showed nothing. Likewise with MBAM yet every time I try to go back to the site Avast reports threat and blocks access. CCleaner has been run multiple times and all cookies removed.
Report to webmaster of the target site advises they have no problem yet threat continues to be reported and the site is blocked to me. In desparation I found a site with apparent knowledge of the threat, F-Secure, ran their free quick scan which turned up 4 items of spyware that were removed and not reported or found by either Avast or MBAM. Still blocked I ran a full scan and turned up two more, all listed as tracking cookies. When blocking continued a further scan of only the reported process with the problem, Internet Explorer, turned up three more tracking cookies yet neither Avast nor MBAM reports any problem and I still can't access the site I want.
What is the fix and why do neither Avast nor Malwarbytes see the problem?