Thank you all for being so kind with trying to help me. I have found nothing in my code and contacted Google about it. I have told them this several times and they have removed the warning, but after a week or two the warning comes back. No other sites or search engines gives me this warning.
My host helped me out and found the code in like 2 seconds. It was in the index.htm file in board/files. It's almost as if it knew where to hide itself. Scanning sites are therefor worthless.