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.

bgribaudo

Attempts to prevent automated SPAM by requiring visitors to answer a question of your choosing in order for their comment to be accepted. Presumably, spambots will be unable to correctly answer this question and so comments they attempt to post will be rejected.
Only regular comments from non-logged-in users are filtered. Pingbacks, trackbacks and authenticated users will not be prompted to answer the verification question.
Privacy Note: This plugin does not call home or communicate with any external servers or services. All processing is done locally within your WordPress site.

Super Simple SPAM Stopper

Prevents automated SPAM by requiring visitors to answer a question of your choosing (plaintext or regex).

Batch Comment Spam Deletion vs Super Simple SPAM Stopper