To help protect your SMF 2.x forum from spam-bots that search for forums to post spam on, go to Admin -> Configuration -> Security and Moderation -> Anti-Spam. (if using SMF 1.x, here’s a mod that does the same thing.)
There you can create new questions registrants must answer and view what’s already added. If the spam-bots have figured out how to answer the current security question, you can replace it with another.
When adding more, be sure to set “Number of verification questions user must answer” to the total number of questions and then logout and test registering with an alternate email address to make sure it’s working.
A lot of forums make the security question specific to their forum or chatroom, so that only people familiar with the topic would be able to answer the question, but of course don’t make it so hard that nobody can answer it.
For example, the answer to a question like “What is the opposite of Up” is probably already known by the spam-bots. But if your forum is about classic cars, you may want to customize your question to be something unique like:
“What company makes the Mustang?”
(of course don’t use this one as now it’s out there).
Also, as soon as you see this spam-bots starting to get through your verification question, it means they have been programs to answer it. Therefore simply change the question. Other form owners will change the questions before spammers get through just to keep things fresh and to keep the spam-bots at bay.
Of course this doesn’t stop human spammers, but those are much more rare than spam-bots. And any human with a brain would see that a forum having a good verification questions is probably not going to tolerate silly spam posts either.
Another (more strict) Option:
Also, another idea is you can disable registration completely and then put a note in the news box or on your website that people should contact you to create an account. Here’s where to edit registration settings:
1. Click the Admin button
2. Then click “Registration” under the “Members” section
3. Click the the “Settings” Tab in the Registration section
There you can disable registration, so that only you (the admin) can register new memberships.