Is there any way to prevent these bots?

[Jacob__mybb_import1]

The registration form already has a CAPTCHA, a security question and anti-bot JavaScript, so either the bots are really advanced, using a CAPTCHA outsourcing service, or they're not bots at all, but people being paid minimum wage to write spam posts.

Can you link to some of the comments? I might be able to code some sort of spam blocker based on the keywords.