Seems to be more and more spam on the forums now. Can you look at upgrading the base software to a newer less exploitable version? I fear one day someone exploits the db and gets all our emails and user information - and all you'll be able to say is sorry.
An upgrade to the entire site, including the forum will come. Other then that even with an upgrade there is nothing that can prevent occasional spam. I pretty much check things daily to make sure it does not get out of hand.