This forum seems to get a bit of spam. I'm sure it is getting tedious to delete.
The captcha that new users have to fill out when registering for an account is obviously no obstacle.
Maybe a policy of always moderating new users' posts could work. So when a new user posts, their first post needs to be approved before it is visible, and thereafter their posts are shown immediately.
I was looking into that yesterday. I've been thinking about upgrading to a new forum as jForum doesn't seem to be under development anymore and lacks a lot of features but I actually like the simplicity of this one and haven't found any alternatives I was that impressed with. The span is annoying and I'd like to come up with a solution. Admin approval of user registrations is not a feature of the forum. Seems like the easiest way would be to change the user registration link to a custom form but then we have to manually create all new users. We also want to implement a single sign on so user can use the same username in the forum, wiki and website once they are all up and running so maybe we'll come up with a solution in the process of that.
Yeah, JForum development looks pretty dead.
No feature to approve new users is odd. Though it sounds like it wouldn't be that hard to hack in... If you happened to know some java developers, that is :-}
Migrating to a new forum and SSO would be a pretty major exercise I expect so I can see the scope of the problem now.