Forum protection from spam

It's become a big problem for forum owners to protect them from spam.
Automated programs are sending their ads in huge quantities today.

We're small community of coders, upgrading forum's source code to prevent spam-programs to post ads at your forums.

Our technique is probably one of the best. There's no need in such ugly methods as 'capcha' or 'secret question'.
For average user there would not be any visible effects. No need to make e-mail activation (that usually makes number of successful registrations less), no even need to make your users register at forums to post messages.

Moved to General. I'd be interested in hearing about this magic bullet you have found. But we keep discussions on the boards, not take them off.

Unfortunately, this site will always require users to login and not allow anonymous postings. Everyone here gets a unique name they pick themselves, don't need 50% of the posts from this user anonymous..