Today, we released an updated version of our Akismet addon to all our clients. It now includes a free Vanilla Forums volume license, so you no longer need to provide your own key. Your own key will continue to work if you entered one previously. If you delete it (Dashboard / Browse Addons / Akismet settings), our key will take over.
Akismet is a dedicated spam-fighting server that will automatically filter all your forum content and user registration requests. We've found it to be an effective tool for combating many types of spam. If you're not currently using it, go ahead and turn it on in your Dashboard under "Browse Addons."
If you're having spam problems on your forum, we also recommend enabling the Stop Forum Spam addon. This is a free third-party service that compares IP addresses and email addresses against a list of known spammers. You can adjust its sensitivity in its settings page. Contact support for help tweaking those values, or if you still get high levels of spam after enabling both those addons.
We really hate spam at Vanilla, and we're constantly working to improve the tools in our arsenal to make sure as little as possible ends up on our clients' forums.