A Very Simple and Effective Captcha

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[View FULL Article] I have a very simple anti bot-spam technique that works extremely well. It requires no javascript, no cookies, no hidden fields, no complicated server weirdness, has negligible overhead, is fully accessible, has a high usability factor and is trivial to implement. Sound good? And it's dead simple too, so read on.

In order for spam to work, it has to be cost effective. In order for it to be cost effective, it has to be automated. In order for something to be automated, it requires a predictable pattern. The fundamental approach to this technique is to to deny the bot a usable pattern, yet make it easy for even the most inexperienced user to use. Since the spam bots use all of our form and predictable choices in form naming conventions (the pattern), we simply add a key that only a human can turn. We require that the user fill out one field with a number that is displayed in plain text. This makes it effective against automated solutions. That's fundamental captcha. Note: It will not, however, prevent humans from manually submitting spam to your form.

In the three years that I've used this, I've gotten a 100% anti spam-bot effectiveness rate over three years and some 20 odd sites. Sites that were being bombarded with hundreds of spams daily suddenly became quiet and good emails get though. I'm a Coldfusion coder, so my example is Coldfusion, but the technique is cross language. I hope it works as well for you.

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