WP-Hashcash

Visitors must use obfuscated JavaScript to submit a proof-of-work that indicates they opened the website in a web browser, not a robot.

If the javascript check fails, WP Hashcash gives three options; it can either put the comment into moderation (default), put the comment in the akismet queue, or delete it.

Installation:

Unpack and upload it to the /wp-content/plugins/ directory.
Activate the plugin through the 'Plugins' menu in WordPress.

Features:

• Blocks all comment spam, but not real comments
• Also prevents most trackback / pingback spam
• Widget support to display spam statistics and edit the configuration
• Works with IE, Firefox, and Safari
• 100% standards compliant XHTML 1.1
• Tested with Wordpres 2.6, Firefox 2, Safari 3, and IE 7
• Akismet compatibility

What is new in this release:

• Support clean interoperation with jQuery and Prototype.
• Protect BuddyPress (BP) signup pages.

Requirements:

• WordPress

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.