Okay, I did two things:
(1) I banned a subnet in Pakistan responsible for a third of the spam we get.
(2) I renamed the register page URL so that automated spambots can’t get to it using the default phpbb URL.
Let’s see what this does.
I believe the problem aren’t spambots, but human spammers. A solution to this would be to check each users first post I belive.
sadly that wont help, as there are a lot of spam bots/persons reply to threads. you often see these as threadbumps with replies that dont quite make much sense