Spammers will spam anything they can post to and not get rejected. They'll spam a password prompt fercrysake.  Don't leave anything open that an unknown/unwanted person can post to, because they will.  Blog trackbacks? (Which bypass moderation). I've cleaned up 1/4 million spams at a time from those until I turned them off.  I hate spam. Hate. Hate. Hate. That's why I got rid of it. You can too.