Unpack in your modules folder (usually /sites/all/modules/) and enable under Administer > Site Building > Modules.
Key features "WP-Hashcash":
· 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
· WordPress up to 2.6
· 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.
Top 4 Download periodically updates information of WP-Hashcash 4.3 script from the developer, but some information may be slightly out-of-date.
Our script download links are directly from our mirrors or publisher's website. WP-Hashcash 4.3 torrent files or shared files from free file sharing and free upload services, including Rapidshare, MegaUpload, YouSendIt, MailBigFile, DropSend, HellShare, HotFile, FileServe, MediaMax, zUpload, MyOtherDrive, SendSpace, DepositFiles, Letitbit, LeapFile, DivShare or MediaFire, are not allowed!