Checks where visitors come from and gives them a warning if they are likely to be comment spammers. For DoFollow and exDoFollow blogs.
Both the list of triggers and the message are customisable, allowing you to control who is shown the message and what they are shown.
It is also possible to redirect potential spammers to a URL of your choice, either immediately (bypassing the warning) or after a certain number of potential spam visits from the same IP address. Note: the number of visits calculated only includes visits where a trigger is tripped (not if the same IP address visits your site via a different method) and includes page refreshes.
Compatibility: I suspect that this plugin will NOT be compatible with WP Super Cache at this point. I will be doing some testing in the near future and, if necessary, changing the plugin so it does work with WP Super Cache.