Comment spam handler systems include
Note: Akismet has received plenty of complaints, some from SEOs, and so not always easy to take seriously, but some seem worryingly legit.
It would be nice to support contribution to anti-spam projects such as
As always, we steal interesting ideas from Sam Ruby. For example:
Example from http://intertwingly.net/blog/2004/01/17/Spam-Update, which came from pressing "Preview" on comment form of http://www.intertwingly.net/blog/1692.html . Comment preview HTML from Intertwingly: IntertwinglyCommentPreview.html.txt
Wikipedia has a useful survey of the issue
Sixapart has an excellent analysis of spam-fighting techniques, oriented towards MovableType, but nevertheless almost a must-read:
The Trac project has documented their own battle against spam:
"Stopping spambots with hashes and honeypots"--Ned Batchelder -- excellent discussion
Defensio - Akismet competitor with less neg rep
wsgiakismet -- probably never to be used: Akismet has a bad rep
SpamLookup - "yes, it's another anti-spam plugin. I would have called it MT-DSBL 2.0, but the feature set grew beyond the name, so a more generic name was chosen. This is a 2.0 release however... the plugin deserves more seniority than a 1.0 release, since it was built of the carcass that was MT-DSBL 1.1."