You can read more at the WP Hashcash plugin page. WP Hashcash is 100% GPL compatible.
WP Hashcash relies on the presence of two hooks in your theme,
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.
Requires: 2.9.2 or higher
Compatible up to: 3.0.5
Last Updated: 2010-3-31
Active Installs: 10,000+
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