Fair call WP. As I have been a forum admin in the past, One thing to try is to restrict all new members to a particular part of the forum until they have reached a set number of posts. Eg start them in ASL or a welcome section in the general forums or something like that and when they have reached say 5 posts, send them into general population. That way you know where the spam is and its easier to know who to get rid of. Its also an effective deterrent to the post loss trolls.