BotScout: Proactive Bot Detection and Screening
BotScout is a free service that helps prevent automated web scripts, known as "bots", from registering on forums, polluting databases, spreading spam, and abusing contact forms on web sites. We do this by tracking the names, IPs, and email addresses that bots use and logging them for future comparison. We provide a simple API (with code samples) that you can use to test forms when they're submitted on your site. There are plugins for phpBB, SMF, VBulletin, and other popular message boards, but BotScout can be used on nearly any kind of web form.