Mollom is an advanced spam filter and CAPTCHA server, implemented as an XML-RPC-based web service, and provided by a Belgium-based company of the same name. Mollom blocks spam by analyzing the content of posts created on protected sites; each post is assigned a rating based on whether its content exhibits common spam characteristics. Posts with a "ham" (or not-spam) rating are completed as normal, while posts with a "spam" rating are blocked. If Mollom is uncertain whether a post is "ham" or "spam", it returns an "unsure" rating, prompting the site to display an audio or visual CAPTCHA challenge to the user, using Mollom's CAPTCHA server. Mollom's use of three result values ("ham", "spam", and "unsure") is a key difference from the binary result values ("ham" and "spam") of many similar services and, through selective CAPTCHA challenges based on the "unsure" result, significantly enhances its accuracy. To further inform its rating system, Mollom combines text analysis, reputation models, and feedback from users of its Mollom Free and Mollom Plus services. Mollom was first introduced in beta form on March 31, 2008. Since that date (as of November 2008), Mollom has blocked over 15 million spam messages. On average, 74% of the posts reviewed by Mollom are spam. In September 2008, Mollom was released in a non-beta form. Current subscribers include several leading online media and publishing companies. Built on a freemium business model, Mollom is available in both free and subscription-only versions. Its subscription-only service, Mollom Plus, provides support for large post volumes and has access to an enhanced backend server architecture not available to Mollom Free clients. Although Mollom was initially developed for the content management system Drupal, a number of other clients are available, including WordPress, Joomla, Radiant, and SilverStripe. A number of developer libraries for common languages are also available, implementing Mollom's API. The Mollom company and service were jointly developed by Dries Buytaert and Benjamin Schrauwen. Buytaert is the founder and project lead of the open source project Drupal. Competitors Mollom competitors include Akismet, Defensio, and Typepad Antispam.