Reducing Comment Spam with Mollom


Mollom logoMoluom is a anti-spam service that plugs in to Drupal and other content management systems via contributed modules. According to their website:

Websites using Mollom send data they want checked to, and Mollom replies with either a spam or ham classification. If Mollom is not certain, it will return an "unsure," typically prompting websites to ask Mollom's CAPTCHA server for an audio or visual CAPTCHA challenge to present to the user.

User Experience

Here's how users will experience Mollom once it's installed on your site:

  1. Most users will be able to post comments without even being prompted for a CAPTCHA, since Mollom's spam detection algorithms will identify the comment as legitimate and allow it to be posted.

  2. Some users will post legitimate comments that resemble spam. These users will be prompted to enter a CAPTCHA to prove they are not an automated bot.
  3. Any users who are unable to pass the CAPTCHA, including automated bots, will be unable to post comments.

Mollom employs a number of strategies to keep as many legitimate users out of group 3. Their CAPTCHAS are fully accessible to the visually impaired.


To install Mollom on Drupal, visit the Mollom project page on to download and install the latest Mollom module. Then register for a Mollom account. For more information, reference the excellent tutorial.

Effect & Conclusions

After migrating from Drupal's Math CAPTCHA module to Mollom, this site has gone from 5-10 spam comments per day to exactly zero spam comments. Additionally the user experience has been improved, as most commenters do not need to respond to a CAPTCHA when posting a comment.


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