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(Completely Automated Public Turing test to tell Computers and Humans Apart) A category of technologies used to ensure that a human is making an online transaction rather than a computer. Developed at Carnegie Mellon University, random words or letters are displayed in a camouflaged and distorted fashion so that they can be deciphered by people, but not by software. Users are asked to type in the text they see to verify they are human.

CAPTCHAs were created in response to bots (software agents) that automatically fill in Web forms as if they were individual users. Bots are used to overload opinion polls, steal passwords (see dictionary attack) and, most popular, to register thousands of free e-mail accounts to be used for sending spam. CAPTCHAs were designed to circumvent non-humans from performing such transactions.

The Battle of the Bots and CAPTCHAs
After CAPTCHAs were deployed in 2001, the felonious bots were updated to analyze the distorted text, enter the correct text and thereby render many CAPTCHA styles ineffective. In an ongoing battle between the bots and the CAPTCHAs, the CAPTCHA text is increasingly more distorted and camouflaged, often making it difficult for humans to decode.

Other approaches have been incorporated to validate humanness; for example, displaying several images and asking what object is common among them, such as a tree or dog. Or, a phrase might be displayed and the user is asked to re-type a word; for example, "Enter the second word in the phrase." See reCAPTCHA, dictionary attack and Turing test.

Type the Word You See
In this early CAPTCHA example from Carnegie Mellon, a random word is camouflaged, and users are asked to type what they see. (Image courtesy of Carnegie Mellon School of Computer Science,

More Obtuse, More Random
CAPTCHAs are increasingly more distorted in order to fool the bots, and real words have given way to random letters and digits. However, just like virus writers, who learn to code their programs more effectively, so do the bot writers... a fun-loving, creative bunch.
References in periodicals archive ?
Identity information is stored by an individual's employer, not in a master database - a more secure and reliable method than other human verification systems.
A proprietary human verification tool inspired by the open-source project Honey Pot, Bearskin leverages an anti-fraud algorithm that protects programmatic traffic against botnets, ad insertions, ad re-directs, OS hacking and other nefarious behavior.
This program requires human verification of a burglary or attempted break-in before police will respond.
People using the 98% figure to justify ending police response to alarms without human verification of a crime (verified response) have failed to perform their due diligence on public safety and industry best practices.
At the same time, it enforces a set of voting rules and allows for human verification that they are followed, according to Gerck.
In the student category, "are you a human" received the top $25,000 student prize for its Detroit-based web startup that uses games for human verification online.
SDL PerfectMatch technology cuts time from the human verification process by automating in-context translation management.
com Brand-Safe Network combines layers of automated scanning and human verification to keep brands safe, while still providing customers with fresh new options for visibility.
Specialized artificial intelligence and algorithms analyze the data and validate the contents, followed by human verification to ensure the highest level of integrity possible.

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