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http://codex.wordpress.org/Combat_Comment_Spam
http://drupal.org/node/14193 - Drupal: Fighting back at Spam
Blog Software
This list is incomplete and in alphabetical order.
- Drupal http://drupal.org
- Movable Type http://www.movabletype.org/
- Serendipity (S9Y) http://www.s9y.org/
- WordPress http://www.wordpress.org/