Worth reading while waiting on Antispam components bundle for Joomla/Mambo
A captcha (an acronym for "completely automated public Turing test to tell computers and humans apart") is a type of challenge-response test used in computing to determine whether or not the user is human. The term was coined in 2000 by Luis von Ahn, Manuel Blum, and Nicholas J. Hopper of Carnegie Mellon University, and John Langford of IBM. A common type of captcha requires that the user type the letters of a distorted and/or obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a captcha is sometimes described as a reverse Turing test. From Wikipedia read more here and here
Hashcash is a proof-of-work system designed to limit email spam and denial of service attacks. It was proposed in March 1997 by Adam Back From Wikipedia read more here and here
