In just a few years, comment and trackback spamming has grown from scarce to massive phenomenon.

It is now more than recommended to have a set of filters capable of recognizing spam from real comments, and that's what provides the Antispam plugin.

To access the antispam module configuration, click on Antispam in the left column. The page is divided in three sections:

Informs you of the number of filtered and published comments, and lets you delete all spam comments in a single operation.

The available filters can be activated individually and placed in the order you like. Filters are applied from top to bottom.

To reorder the filters, drag and drop them with your mouse in the desired position. To enable or disable a filter, tick or untick the corresponding checkbox. Click on Save to apply the changes.

These are links to RSS feeds that let you track spam comments and published comments.

Some filters have their own configuration interface accessible via a link located on their lines in the filter list.

This filter checks whether incoming trackbacks include a link to the post they are trackbacking. If it's not the case, the trackbacks are automatically denied access, i.e. they won't be listed in the junk comment list.

This filter allows you to add IP addresses to a black list or a white list manually. If a comments come from a blacklisted IP address, it will be immediately classified as spam. And if a comment comes from a "whitelisted" IP address, it will be considered as safe and the other filters won't be applied.

To add an IP address, first choose the "black list" or "white list" tab then add the address.

The "Global IP" checkbox is available is you are super administrator, and it allows you to apply this setting to all the blogs of your installation. Global IPs are displayed on a green background.

This one filters comments when the author's name, email address or URL, or the content of the comment, includes certain defined words.

As for the IP address filter, you simply need to add the words you want to block to the list. If you have the required permissions, you may also add global words that will trigger the filter on all blogs of your installation.

IP Lookup is a filter that checks the IP address of the comment author against shared IP lists called DNSBL (or RBL). You may add as many servers as you like, separating them with commas.

The filter uses sbl-xbl.spamhaus.org et bsb.spamlookup.net as default servers.

This filter works a bit like IP Lookup, except that instead of checking the author's IP address, it checks whether the links included in the comment (including the author's site) are featured on the "multi" list of surbl.org. This filter cannot be configured.

Akismet is a spam filter service provided by Automattic that yields excellent results. To activate it, you need an "API key" that you will enter in the Akismet API key of the filter's page.

To get this most desirable key, you need to sign up for a wordpress.com account. Once your account is created, you will receive a welcome email containing the key, which will also be available from your wordpress.com profile page.

Learn more.

To use the same Akismet key on all the blogs of a single installation, you should set blog_id to null for the setting_id 'ak_key' in the dc_setting table.

This will make the key available to all. If you wish to prevent other users from changing it, you can set the DC_AKISMET_SUPER constant to true in the configuration. This will block Akismet's interface to all users that are not super administrators (but enabling or disabling the filter will still be possible).