Mar 12th, 2014
From the project page, "Implementation of http:BL for Drupal. http:BL can prevent email address harvesters and comment spammers from visiting your site by using a centralized DNS blacklist. It requires a free Project Honey Pot membership. This module provides efficient blacklist lookups and blocks malicious visitors effectively.
http:BL has been adopted for use to enhance protection on Drupal.org"
Also, see Honeypot module.