We have a new feature just rolled out today: reCAPTCHA support. If you haven't stumbled upon it before, it's a great method for preventing spam on things like forums. It works by asking the user to type in two words that are displayed in an image. It's very easy for a real live human to successfully enter the correct words, but very difficult for an automated spambot.
There's lots of information on reCAPTCHA itself on their web site
. reCAPTCHA is particularly good as it helps digitize books, so it's doing something useful as well as providing spam protection. That's partly why we chose to use this existing service rather than one of our own invention.
The new feature is available both as a board-wide setting in Edit Board Settings, and as a per-forum setting, so you can choose which class of users have to perform the reCAPTCHA check. We recommend you have it set to Guests, so that anyone who isn't logged in will have to perform the reCAPTCHA check when they try to post. This should vastly cut down on spammers.
We will be automatically enabling this option (just for Guests) on all boards on 29th of May 2009. If you don't want it to be enabled, simply change the setting to "Disabled" right now, and it won't be enabled on 29th. If you choose the setting you want now, you'll have it exactly as you want it and no changes will be made to the setting on 29th - it'll only be auto-enabled for Admins who haven't changed the setting at all.
I hope this explained the feature clearly. If there are any questions, fire away.