In the on-going war against spam, I’ve noticed spammers starting to use a new tactic. They simply copy and paste previously posted legit comments that have passed all spam filters, modify them just a little by tacking on a link to their spam site, and then re-posting the comment. The logic here is that the legit parts of the comment will outweigh the spammy payload, and thus allow the comment through. This type of attack seems to be happening more frequently now, so I’ve made a simple update to my spam pre-filter to help cut down on these types of spam.

The Simple Spam Filter for WordPress now includes an additional rule to block any comment that is very similar to a previously posted comment. It uses PHP similar_text() function, and if someone tries to post a comment that is over 75% similar to a previously posted comment, then that person’s comment will be blocked.

And as a (potential) added benefit, this plugin will help reduce the “noise” in your comments, by forcing your visitors to say something new… kinda along the lines of xkcd’s chat moderator bot which helps manage the signal-to-noise ratio in their chat rooms.

This release also includes a small re-organization of files, in order to support WordPress’ new plugin auto-updating feature. Please download the upgrade version if you have a previous version of the plugin installed, otherwise, go grab the 0.6 version here.

As with the previous release, this plugin will work in conjunction with the reCAPTCHA service to help ensure comments that get flagged as spam are really posted by humans (eliminate false positives).

Download the Simple Spam Filter >

Here’s a screen shot of the new filter in action: