ONLamp.com: Securing Web Forms with PEAR's Text_CAPTCHA: "Securing Web Forms with PEAR's Text_CAPTCHA
by Marcus Whitney
When you have publicly available forms on the Web, you are always prone to attack by people who want to use your application for their own purposes. Forums, polls, guestbooks, and blogs are the popular places for robots to try to generate inauthentic posts on your site. Many sites, such as Yahoo, now employ CAPTCHA. CAPTCHA, or 'completely automated public Turing test to tell computers and humans apart,' is a project of the Carnegie Mellon School of Computer Science that sets out to determine if a human or a computer initiated a request. CAPTCHA technology enables you to discern human requests from computer generated requests on the Web, where such a distinction is difficult."