A plugin which identifies and blocks comment and trackback spam on blogs with integration to various blogging systems.
BBC News - How spammers are targeting blogs
Spammers are turning their attention to weblogs, angering technology analyst Bill Thompson. He calls it "flyblogging."
An open source a PHP-based solution for blocking link spam and the robots which deliver it by analyzing the delivery method as well as the software the spammer is using instead of looking at the content of potential spam.
Blog Spam Database
Database of URLs and phrases often used by spammers, along with links to related resources and a discussion forum.
A spam protection service for websites.
Comment Spam Wiper
Comment protection for your site.
Google - Keeping comment spam off your site and away from users
Recommendations from Google Webmaster Central on captchas, automatic filtering, and other anti-spam tactics.
Internetnews.com - Six Apart Trains Guns on 'Comment Spam'
The blog tools vendor Six Apart plans to roll out an open online authentication system to fight the growing phenomenon of comment spam.
Jeremy Zawodny's Blog - Guerilla Tactics Against Blog Comment Spammers
Suggestion that bloggers create posts that target the same spammy phrases that blog spammers want Google to find.
Jeremy Zawodny's Blog: Using mod rewrite against comment spam bots
Very short tutorial.
Kalsey Consulting Group - Comment Spam Manifesto
Weblogger crystallizes the thoughts of many in declaring a cyberwar on those who inappropriately post in guestbooks and weblogs.
Instead of CAPTCHA we insert an advertising image.
Learning Movable Type: Concerning Spam
Types of spam seen on blogs.
NBC News - Spammers now clogging blogs, IM
Spam has never been limited to e-mail. But now, commercial pitches are increasingly popping up in online chats, instant messages, cell phones with text messaging and weblog comments.
No Guestbook Spam Anymore
Offers instructions for webmasters for avoiding and eliminating spam in guestbook.
OJR : Bloggers Declare War on Comment Spam, but Can They Win?
"Here's a look at the battle so far."
Project Honey Pot
A free, distributed service that tracks comment spammers and allows website administrators to block them through its http:BL service.
Spam huntress dissects blogspam.
Stop Forum Spam
Provides statistics and various information about persistent spammers on message boards and blogs.
Provides an open source antispam plug-in for Movable Type and WordPress.
Wired - Googlemania: The (Evil) Genius of Comment Spammers
Background of the phenomenon of comment spam and how bloggers responded.