Akismet
Thanks to Zend_Service_Akismet, Akismet Spam protection for comments has been added to Tiki.
Use Akismet to filter comments: If enabled, Tiki will use the Akismet spam filter for comments.
If enabled, you can also filter spam comments for registered users.
You must obtain an API key from http://akismet.com/
Also see: Spam Protection