WordPress.org

No More Spam

WP Hashcash is an antispam plugin that eradicates comment spam on WordPress blogs. It works because your visitors must use obfuscated javascript to submit a proof-of-work that indicates they opened your website in a web browser, not a robot. If the javascript check fails, WP Hashcash now gives you three options; it can either put the comment into moderation (default), put the comment in the akismet queue, or delete it.

You can read more at the WP Hashcash plugin page. WP Hashcash is 100% GPL compatible.

Features

1. Blocks all comment spam, but not real comments
2. Also prevents most trackback / pingback spam
3. Also protects signup pages for WordPress (WP), BuddyPress (BP), and WordPress Multi-User (WPMU)
4. Widget support to display spam statistics and edit the configuration
5. Works with IE, Firefox, and Safari
6. 100% standards compliant XHTML 1.1, works with jQuery and Prototype
7. Tested with Wordpres 2, Firefox, Safari, IE, and Chrome
8. Akismet compatibility

Limitations

WP Hashcash relies on the presence of two hooks in your theme, wp_head and comment_form. If your theme doesn't include these actions, you will need to add them immediately before the end head and end form tags respectively.