As your blog becomes popular, one problem that seems to cause a lot of concern is comment spam. You must have seen them, comments with long lists of URL’s that advertise items that you would rather do not appear on your blog, or medicines that you are not interested in buying, or other similar comments that have no relation to your blog. What do you do ? You search for some way to stop these spam. Akismet is one option, but even with Akismet, you get a lot of spam that needs to be cleared out regularly. Once I missed out clearing the comment spam from Akismet for several weeks, and when the auto-cleaning for Akismet happened with around 20,000 such spam comments, it created a performance hit on my shared server (and the steps I had to take after that are not something you want to repeat on your own blog – I had to get my account re-activated).
Read (and download) the plugin at this location (link)
Bad Behavior prevents the spam from even making its way onto your server or blog, thus ensuring that you do not have to fish among all the comments filtered by Akismet to search for genuine comments. From the site:
Bad Behavior complements other link spam solutions by acting as a gatekeeper, preventing spammers from ever delivering their junk, and in many cases, from ever reading your site in the first place. This keeps your site’s load down, makes your site logs cleaner, and can help prevent denial of service conditions caused by spammers.
Bad Behavior also transcends other link spam solutions by working in a completely different, unique way. Instead of merely looking at the content of potential spam, Bad Behavior analyzes the delivery method as well as the software the spammer is using. In this way, Bad Behavior can stop spam attacks even when nobody has ever seen the particular spam before.