Top Six Drupal Modules to Prevent Spam

There are some wonderful Drupal modules that can help your site in its quest to fight spam. If you are looking to protect your email addresses from harvesting or just want to eliminate spammy posts and comments, this list is for you. Here are six of the top Drupal modules for spam prevention.


Mollom is what is referred to as an “intelligent” web service.  It integrates well into a variety of websites due to the content that it monitors.  Mollom will not only analyze the quality of the comments being posted to your site, but it will also scan blogs, messages in contact forms, forum posts, and more. 

Mollom basically splits content into two categories: ham or spam.  Ham is desirable content, and spam is undesirable.  Mollom screens all of the incoming content to make sure it is of the ham variety, and then posts it to the website.  Mollom uses a history of activity on all sites within its network to help determine whether or not content is spam.  Post content and the poster’s reputation is taken into consideration.  In other words, Mollom is like a human moderator on autopilot. 

If Mollom is unsure if content is spam, it will go to a secondary line of defense – the CAPTCHA challenge.  The user will be given an audio or visual CAPTCHA challenge that they must complete for the content to go live.  This not only prevents unsure content from going live, but it also keeps it from being misdiagnosed and classified as spam.  If spam somehow makes its way onto the site, the site can report it to Mollom for future reference and to benefit all of the sites within the network.  Mollom is available in Free, Plus, and Premium.



The reCAPTCHA module is rather simple in its form but highly effective.  CAPTCHA programs generate simple tests that humans can pass but most computer programs cannot.  Distorted text is a common CAPTCHA example that will generate a couple of words on-screen that the user must type for acceptance. 

CAPTCHA integration works well in various situations, making it an attractive service for a wide range of sites.  It can prevent spam emails and comments, be used to verify submissions in online polls, protect registration on websites, and more.  The reCAPTCHA service digitizes actual books and scans their text.  The text is difficult for computer programs to decipher as it is placed onto an image.  Adding reCAPTCHA to your site adds a solid line of defense against spambots, as it requires human input.  Not only can you protect the content that gets posted on your site, but you can also protect your email address.  reCAPTCHA will ask a user to solve a CAPTCHA in order to view your email address.



SpamSpan is a Drupal module that helps protect email addresses on your site from being harvested by spambots.  It works by obfuscating email addresses using JavaScript.  This not only protects your own email address, but also any email addresses belonging to your users that have been posted.  The obfuscation of email addresses helps to promote more interaction among visitors, since the worry about email address harvesting is diminished. 

SpamSpan is compatible with almost all browsers on the market.  If compatibility is an issue, SpamSpan will degrade gracefully.  While most email obfuscating services require that JavaScript be enabled on the client side, SpamSpan does not.  It will offer a clickable link to the email address if JavaScript is enabled.  If JavaScript is disabled or not supported by a browser, the email address will still be visible, but presented as user1 [at] example [dot] com. 

While the obfuscation technique used by SpamSpan is not completely foolproof against harvesting, it does help, as many spambots will not attempt to collect email addresses that have been hidden using JavaScript.  With that being said, SpamSpan is very concise and easy to implement.  Best of all, it is free and available for personal or commercial use.


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While CAPTCHA is considered to be an effective way to combat spam, there are certain situations where the traditional image CAPTCHA is not desirable.  Situations where CPU restrictions or bandwidth restrictions exist are just two examples.  The CAPTCHA Pack module takes various CAPTCHA types and integrates them into a solid package that can be easily implemented in different situations.  The module is lightweight and easy to configure.

Here is a list of the challenges included in CAPTCHA Pack:

  • A math CAPTCHA that will ask a simple question like “one plus two equals?”  The math CAPTCHA can be configured to include addition, multiplication, and more.
  • Various text-based CAPTCHAS.  The user may be asked to pick which word does not belong in the sequence.  They may be asked to pick the correct word from a phrase.  They also may be asked to enter the missing letter into a word.



The appropriately-named Spam module allows you to protect your site from spam without having to soliciting the help of third-party services.  The module incorporates several spam filter modules into one.  The filter modules collaborate to help determine whether or not content is legitimate or if it is undesirable spam.  The content gets rated on a scale of 1 to 99.  A 99 score means that the content is 99 percent likely to be spam, while a 1 score means that it is only 1 percent likely to be spam.  The scores released by the different filter modules are averaged, and the final overall score determines the content’s acceptance.

The filters are headlined by a Bayesian filter that auto-learns and analyzes the words in new content.  The Bayesian filter can also detect spam in any language.  A URL limiter auto-learns spammer websites and blocks any content linking to them.  The Node age filter associates comments on old content as spam, while the duplicate filter blocks duplicate posts and bans IP addresses associated with them. The SURBL contains a blacklist of spamming URLs.  Last, but not least, Spam allows you to create custom filters using powerful regular expressions.

To prevent the loss of misdiagnosed content, the Spam module will notify the administrator and user if any content was marked as spam.  This helps in case any confusion arises over missing content.  Users also have the ability to provide feedback if their content is incorrectly marked as spam.



Invisimail is another solid module for anyone looking to protect email addresses posted on their site from harvesting.  While its never recommended to post email addresses on public forums and similar sites, the necessity to do so does happen on occasion.  Invisimail offers a barrier of protection to make this practice less risky.

Invisimail converts email addresses to ASCII code.  Additionally, a concatenated JavaScript write command is used to optionally write the addresses to the page.  Although their HTML source is hidden, the email addresses will still appear on the page in their normal visual format.  This allows them to still be usable by actual human visitors, but keeps them shielded from spambots looking to harvest.


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