Is there a way to make one of the forums available to new signees, and the rest available once an admin gets a chance to review and approve their account? That way, we will know that going into that forum runs the risk of getting spam, but if we are careful we can pick out the new users that are legitimately here to ask a question they are in a hurry with and answer them.
It would probably be easier to take legitimate posts and move them out into the proper category then delete the "free for all forum" than it would be to clean the spams one at a time.
Just throwing this out there. I don't think we should shut down new memberships.