Snowball Effect Plugin – Spam Blocker
Mark has come up with an innovative way to handle those nasty spam comments that sometimes make it past the spam words list:
As described on Mark's blog:
The plugin works by checking to see if there are any comments in moderation or that have been posted in the last 24 hours that have the same IP address, e-mail address, comment body, or URI as the current comment being submitted. If there are more than 5 (default) comments that match any of those fields, the comment is sent to moderation, and all similar comments within the past 24 hours are retroactively sent to moderation. This check only occurs if the comment gets past WP’s built-in moderation.