Stopping Spam on WordPress Blogs
Whent it comes to spam with WordPress and other blogging platforms there are generally two types, trackbacks and comments.
To deal with the trackback spam go to Settings > Discussion and make sure that “Allow link notifications from other blogs (pingbacks and trackbacks)” is unchecked. If someone wants to link to a page or post on the site they can grab the URL and paste it in. Doing this prevents spambots from blitzing your site with trackbacks.
To deal with the comment spam make sure that you have activated Akismet, it’s one of the two plugins that comes with WP by default and it is really good at catching over 90% of the spam. For example, on my blog out of the last 4861 comments I’ve had 4,713 spams caught by Akismet, it let through 148 legitimate comments, and missed only one with an overall accuracy rate of 99.589%. That’s good stuff.
The other plugin I recommend for stopping spam comments is SI Captcha Ani-Spam by Mike Challis. This puts a captcha on the login and/or comments.