Plugin: No Duplicate Comments
Prevent visitors from leaving duplicate comments/pingbacks/trackbacks to a post.
Details can be found at the plugin's homepage:
All of my plugins can be found at:
* Requires at least WordPress 1.5.
* A duplicate is a comment/pingback/trackback that meets these criteria:
Its contents match that of another comment in the same post
Either the commenter's name or e-mail address (if provided) also match.
I won't claim this approach won't lead to false-positives, but as far as I'm concerned it's reasonable.
* If a comment is deemed to be a duplicate, an error page is displayed to the user indicating as much.