Pippin Williamson

Modifies the Empty Spam action in WordPress to process the spam deletion in batches, allowing you to delete thousands or even hundreds of thousands of spam comments at once without killing your server.
Have you found a bug or have a suggestion or improvement you’d like to submit? This plugin is available on <a href="https://github.com/pippinsplugins/batch-comment-spam-deletion" rel="nofollow ugc">Github</a> and pull requests are welcome!

Batch Comment Spam Deletion

Modifies the Empty Spam action in WordPress to process the spam deletion in batches instead of all at once.

intermod

Comment SPAM Wiper checks your comments against the CSW web service to see if they are SPAM or HAM. 
If a SPAM comment is detected it is automatically moved to SPAM folder. If a SPAM comment is not detected and you manually 
mark it as SPAM, Comment SPAM Wiper will learn and in the future it will detect it as SPAM. CSW learns and improves detecting blog SPAM as it goes.
You will need an API Key (http://www.spamwipe.com/signup.html) to use it. The API Keys are FREE of charge.
<h3>License and Warranty</h3>
The Comment SPAM Wiper plugin for WordPress is open source and 
is licensed under the GPLv2.
This program is distributed in the hope that it will be 
useful, but WITHOUT ANY WARRANTY; without even the implied 
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR 
PURPOSE. See either the GNU General Public License for more 
details.

Comment SPAM Wiper

Comment SPAM Wiper is a distributed solution for fighting comment SPAM (aka blog SPAM) that automatically filters the SPAM comments.

Batch Comment Spam Deletion vs Comment SPAM Wiper