WordPress.org

1. Unzip and upload to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Remember to delete WP-Cache if you have that plugin active. Otherwise, you may not see effect of this plugin immediately.
4. If you want to add nofollow in comment author's url's whose link point to blacklisted sites, add at the end of the code in 'nofollow-reciprocity.php' file this line: <?php add_filter('get_comment_author_link', 'wp_nofollow_reciprocity', 999); ?>

That's it! Watch the blog traffic statistics.