The hashcash algorithm

Yeah, it has a weird name, but it's one of the most interesting (and effective) anti-spam algorithms out there: Hashcash. How does it defeat spam without the end-user even knowing a spam check is taking place? Read on.

No, this isn't a Bayesian filter-like algorithm; this is something completely different. Hashcash involves inserting a piece of Javascript code into your site's comment form that sends a server-generated key as part of the comment form's data. If the sent key doesn't match the one the server sent as part of the comment form, the comment is marked as spam and not posted. Amazingly simple. And this all happens behind the scenes, without your users even knowing a spam check is going on!

Now, this algorithm works solely on the premise that spambots are incapable of running Javascript, so if spammers come up with a spambot that is capable of running Javascript, Hashcash would be in hot water. But again, no such spambot currently exists, so Hashcash is currently a viable spam-blocking algorithm.

I think Hashcash is such I good idea, I'm going to give it a test run on this site using the WP Hashcash plugin for WordPress. Hopefully I won't have to manually deal with spam for a long time to come. :)