Using mollom with Drupal
We have recently started using Mollom on our Drupal site. Mollom is a clever anti spam service, that combines auto SPAM detection techniques with a normal CAPTCHA. The idea is simple, Mollom will check form submissions, if it thinks something is SPAM then it will prompt the submitter to complete a CAPTCHA. This means that you don't risk losing valid submissions to an over aggressive SPAM filter, and you don't risk scaring off users with an un-necessary CAPTCHA.