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If it's definitely not a referrer issue, you need to talk to your host. If you are on a shared server it's possible another client has wysiwigPro installed and it has been used as a gateway for an exploit.
The recent Santy webworm gained access through vulnerable phpBB forums, but it often affected every PHP and ASP site on the same server, even those who were not running phpBB.
If the server is *still* under attack, your host will need to resolve the problem before anything that you do will help.