“Bad Behavior is a set of PHP scripts which prevents spambots from accessing your site by analyzing their actual HTTP requests and comparing them to profiles from known spambots. It goes far beyond User-Agent and Referer, however. Bad Behavior is available for several PHP-based software packages, and also can be integrated in seconds into any PHP script.”
phpbloggingsueblimely sueblimely
This is a pretty cool plugin, might have to give this a shot =D
Till then,
Jean