http://www.stopforumspam.com/
http://twitter.com/StopForumSpam
https://github.com/arminrosu/StopForumSpam-PHP-Lib
https://github.com/emberlabs/sfslib
http://tiki.org/tiki-view_forum_thread.php?forumId=4&comments_parentId=48565
https://packagist.org/packages/noop/stop-forum-spam-bundle
It is associated with ZB Block