Bayensian spam filter and/or captcha for open boards

[greggman]

An open board is supposedly 10 times more effective for getting people to participate than a board that requires registering

But, unfortunately an open board is easy target for a spam bot.

It would be great of there was a Bayensian spam filter for posts as well as a catchpa so you could leave the board open but still stop the spam

[MathieuDemers]

http://www.simplemachines.org/community/index.php?topic=110948.msg712316#msg712316