Comment spam was mentioned in the chapter on comments. Apart from turning off the ability for users to add comments, how can you prevent comment spam? One way is to install an anti-spam plugin.
Akismet is a system which automatically detects comment and trackback spam. It is an external service run by Automattic, the company that provides WordPress.com.
Akismet can be installed for free on non-commercial websites by installing a plugin that interacts with the Akismet mothership using an API key. You can review the spam it catches under "Comments".
There is an overview on how to use Akismet on the WordPress Codex site here: http://codex.wordpress.org/Plugins/Akismet
Other spam plugins
There are other plugins and ways of stopping comment spam - too many to include everything here, so we will look at two: Captcha plugins and the wp-Spamfree plugin.
Captcha is a system which asks users to copy a short sequence of letters and numbers which is displayed as an image, therefore only readable by human. This prevents robots from posting comment spam.
If you search for "captcha" in the plugins page of your WordPress site, you will see quite a few alternatives that you can try.
In this example the SI-Captcha plugin is used: http://wordpress.org/extend/plugins/si-captcha-for-wordpress/.
After installing the SI-Captcha plugin, users see an addition to the comment form:
The default settings for the SI-Capture plugin seem to be effective.
Navigate to Plugins and then SI-Captcha Options in the lefthand menu of your Dashboard.
Here, you are able to set the different users and parts of your site where the form captcha is used.
Other anti-spam plugins
- Bad Behavior plugin: http://wordpress.org/extend/plugins/bad-behavior
- Growmap: http://wordpress.org/extend/plugins/growmap-anti-spambot-plugin/
- Spam Free Wordpress: http://wordpress.org/extend/plugins/spam-free-wordpress/faq/