Apparently the bots have been able to overcome the Captcha filter in new user registrations, and this explains why all the spam recently:
http://www.phpbb.com/community/viewtopic.php?f=46&t=1437125#p8563395"Unfortunately, it appears as if automated spambots have become able to crack the 3.0.4 CAPTCHA. 3.0.5 introduces several new changes to the CAPTCHA that will hopefully deter these spammers. Until then, there are numerous things you can do to limit or completely stop your spamming problems."I have a MOD that I will be installing that should be able to stop the automated bots. Supposedly, just adding one or two different requirement fields to the registration process throws off the automation of the bots, so I am going to have the registration process ask a simple question that a human will be able to answer easily.
I was assuming that these recent spammers were human, but I understand now how it's profitable if it's an automated bot able to log in and post thousands and thousands of spams per day to boards like this one. Let's see if we can stop them.