I think I have a virus/malware but I can't remove it

For some reason a lot of the links I click after my Google search redirects me to some advertisement sites.

So I run AVG and I find a bunch of viruses and I delete them and scan it again and I get no more results but I'm still getting redirected. I then go and download Malwarebytes' Anti-malware program and run that and find 3 more threats and I also fix it. Just to be safe I run the online Trend Housecall program and find one more threat.

I'm thinking now that I got everything but Firefox is still fucking redirecting. The redirecting only happens sometimes so that's kind of odd. Also, my bookmark links never redirect me, only when I do Google searches.

I am on Windows 7 Ultimate and I have Firefox 3.5.5 and I updated my AVG and everything. I don't know what else I could do.

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You may be seeing this attack (description):

http://blogs.zdnet.com/security/?p=4947

Does that sound like what you're seeing?

If this is it, then it's not your computer but the website. Don't fall for the fake security programs or whatever adverts. Better yet, install the Noscript extension in Firefox (and learn how to use it) and you won't even see this problem.