This happened to me recently, and got help over at 3dCommune. Download Spybot @ http://www.safer-networking.org/ and before you run it get the updates then search for problems. This is what is called browser hijacking, you get it from looking at porn or using p2p software (not just kazaa but any file sharing legal or not) now I am not suggesting anything cause it could have come from emails or what have you but porn (how I got mine) and p2p are the top causes.

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