Luis von Ahn, Manuel Blum, Nicholas Hopper, John Langford, 2000

Despite what some people think, a CAPTCHA is not intended to prevent hackers from cracking a Web site. It is a program that protects Web sites against automated bots. Humans can pass a CAPTCHA test, but current computers are unable to read the distorted text. The acronym CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. In the future computers may be smart enough to pass the Turing test. That way CAPTCHAs won’t outsmart them anymore. And when that happens…….run!