The next time you're hacked, put a screen capture on your site and link to it here so we can see what the hacker has done. I don't see anything obviously wrong with your site.
I can tell you this, if the hacker has planted a hacking tool anywhere on the server hosting your site, he can view any file on your site, even if it's in a parent folder above the wwwroot. And since the Access MDB for the forum must be in a folder that the anonymous IUSR account can read and write to, such a hacker can not be prevented from modifying the MDB.
Check your site for hacker-related files. Check the WWF upload folders for files other than the permitted jpg, jpeg, gif, zip, and rar (and couple others I can't remember). If you see asp, exe, vbs files in your upload folders, chances are good that WWF was the vector. If such files exist outside the upload and especially outside the forum, chances are better that WWF was not the vector and some other site on the same machine was the actual source.