[chrishajer]

Maybe the restrict registration plugin would help:

https://bbpress.org/plugins/topic/44?replies=3

Or even this admin add user plugin:

https://bbpress.org/plugins/topic/29?replies=3

Or this approach:

https://bbpress.org/forums/topic/fight-against-auto-register-robot?replies=1#post-3431

Or this:

https://bbpress.org/forums/topic/registration-spam-038-akismet?replies=7#post-6274

I have never had a spam comment posted, but I get lots of spammers who register. I just nuke them every couple of days.