Akismet is an important plugin for WordPress. Akismet checks WordPress comments against the Akismet Web service to see if they look like spam or not and lets you review the spam it catches under your blog’s “Comments” admin screen.

Major features in Akismet include:

• Automatically checks all comments and filters out the ones that look like spam.
• Each comment has a status history, so you can easily see which comments were caught or cleared by Akismet and which were spammed or unspammed by a moderator.
• URLs are shown in the comment body to reveal hidden or misleading links.
• Moderators can see the number of approved comments for each user.
• A discard feature that outright blocks the worst spam, saving you disk space and speeding up your site.

It is important to clean out the spam contents. Here is the criteria for the spam.

(1) If they are not addressing the content with your post in a way that shows they read it
(2) If they are dropping a link to their site that is completely irrelevant
(3) If they are using something other than a real name for their name (ex. website name)

Spammers can be tricky and Akismet plugins may not be able to prevent all of your spam, sometimes, you still need to manually check and delete spammer comment.