Habeas thought they had a clever idea: copyright a little haiku, consider any mail that has the haiku to be not spam, then sue any spammer who violates their copyright.
What a dumb idea! The problem is spamassassin treats this mark as strong evidence of not-spam (-8.0: +5.0 required to be spam). So of course a bunch of spammers are including it to slip past spam filters. My carefully tuned spam filters started failing recently because of this. Sure, some day maybe a copyright lawsuit will bring some relief, but that's years away.
I'm not the only one with this problem: Anders Jacobsen, no such weblog, truerwords, uncle dirtae, etc. The problem is that spam is an arms race: as soon as the spam filters impolement a technique the spammers find an exploit. 'Test for this magic string' is awfully easy to exploit.
Solution? score HABEAS_SWE 0.0.
Update 2004-03-15: a spamassassin developer contacted me. They are working on a fix that sounds good.