PHP-nuke quick fix
I’ve noticed that some PHP-nuke sites have word filters. And when those filters get tripped, they break URL’s.
So my suggestion is to load those puppies up with as many rude words and permuations of rude words you can, to at least break some links while you clean up the mess left by the spammers.
Shutting down comments for the duration would work too (note, I haven’t used PHP-nuke, so don’t know what that would take).