Bad Behavior is a cross platform spam blocker that works well with other anti-spam solutions you may be using. It was created to block link spam and robots that spam your website.
Using the plugin is very straight forward. It works right out the box though you can change some settings if you wish such as the strength of your security. By enabling strict checking you will block more spam but you are more likely to block legitimate requests on your website too. You can also block requests from other websites; this reduces spam however this can stop services such as OpenID accessing your website.
Spammers are shown an error message instead of your website. There is an error key in the error message that humans can use to gain access to your website should they be blocked accidentally.
The plugin provides a list of every agent that was blocked. The reason why the agent is blocked is also displayed. For example, the agent may be on a blacklist or there may have been missing information.
I tested Bad Behavior on my test blog however I’ve not used it on a live website as yet; so I cannot say first hand how effective it is. It does seem like a useful way of blocking known spam bots from accessing your website and leaving junk messages. It’s worth trying out if you are having problems with comment spam.