Recently there has been an increase in the number of spam users signing up to the forum. This has caused a few spam posts to make it into the forum for a few hours until I can remove them.
To fix the issue of spam users registering with the forum, the forum captcha difficulty has been increased. Previously a missing image library on the server was preventing the forum captchas from properly being generated at the higher difficulty levels. Also we made a few custom changes the to the forums registration.php file to prevent automated registrations that bypass the proper sign up page.
Until I can be sure that this has resolved the issue of spam users signing up to the forums, I have changed new user registration to require approval by the admin.
Hopefully this defeats the spam bots.