PM Spam Crashing MySQL

[محروم.كوم]

My site went down last night, at first it seemed that a MySQL restart would fix the problem, but it soon became apparent that something else was going on. I received this message from our managed dedicated server admin:


Quote:
I believe I have found the cause of the instability. You have an email form
hosted at http://www.mysite.com/forum/private.php
Is that correct? I just cleared more than 1000 spam messages and bounce-backs
because the mailer there is being used to send 'Adult Friend Finder'
spam. You'll want to add a CAPTCHA to this page to prevent auto-spammers
from abusing your mail server.

Unfortunately, the spammer has caused your database server to become unstable
and your database files to become corrupt. I'm working to repair these
now, but the load on the server is still high- you may wish to suspend the
vBullitin mail page that sends mail with the subject 'New Private Message'.

The thing is, we have PMs disabled for users with less than 50 posts (I know, crazy), and I don't see any spam PMs in the recent history using "read PMs."
I've temporarily solved the problem by using .htaccess to redirect private.php to a static page. Anybody have ideas about how to solve this problem? __DEFINE_LIKE_SHARE__