Spam Filters That Fight Back

Paul Graham writes extensively on the Spam Wars.  His
article "A
Plan for Spam" explains Bayesian filtering, where an "intelligent"
filtering agent is continually learning according to your actions and corrections
of its efforts.

"The Achilles heel of the spammers is their message. They can circumvent
any other barrier you set up. They have so far, at least. But they have
to deliver their message, whatever it is. If we can write software that
recognizes their messages, there is no way they can get around that."

Now Graham has posted another
excellent article on the latest developments
in the Spam Wars and anti-filtering techniques.

"As I mentioned in Will
Filters Kill Spam? , following all the urls
in a spam would have an amusing side-effect. If popular email clients
did this in order to filter spam, the spammer’s servers would take
a serious pounding. The more I think about this, the better an idea
it seems. "