In just over a week, MT-Blacklist has already automatically blocked over 430 spam comments for this blog. I only had to moderate one by hand and I was notified by email.

MT-Blacklist, a Movable Type plugin, uses a list of keywords and URLs to block comments. This works because spammers are trying to improve Google rankings of certain web sites by flooding comments with links, so the target URLs are obvious. The keywords are shared by the MT-Blacklist plugin and distributed around to other MT-Blacklist installs so that comments containing the keywords are automatically blocked for other people. I suppose you could consider it a kind of distributed moderation -- and it's working really well!

It works so well that the author won a contest for best Movable Type plugin and got a brand new Apple G5, which he sold to pay off debts.

There are email spam blockers that also work on the same principle. The more information that is moderated and shared the smarter the filter gets, which leads to less false positives. It sure is better than an isolated spam filter: the whole network can respond almost at the same time.