SpiderSquash analyzes client behavior and determines whether or not a client is a legitimate user or a malicious bot.
WordPress Security Plugin - Perform over 23 Basic Security Activities for your blog and get a free malware scan at the same time! See more details at
The plugin provides the next generation in captcha, BotProof Captcha 2.0, to a WordPress blog comment form. It is currently version 0.9.6.8 Beta.