We have a PHPBB forum running for a few years with admin approval of newly registred users. New users can not post on the forum untill we approve their new account.

So I get an e-mail for every new registration, and sometimes there are spambot registrations amongst them. But untill yesterday this was only a few a year, but overnight I got 32 (!) new registrations and they keep rolling in every 15 minutes or so.

I run the latest PHPBB version and spambot countermeasures are on. We first had the ReCaptcha option, but that didn't work well. Then we changed it to a Q&A version and that worked. I changed the question an hour ago, but the new spam registrations keep happening, whatever I do.

Help!