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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 ?
Modern CAPTCHAs provide a snapshot of the challenges of visual perception, and solving those in a general way required us to understand how the brain does it," said Vicarious co-founder Dr.
Users complete these little games faster than other CAPTCHAs, with no frustrating failures and no typing.
We want to present our customers with simple, engaging solutions, and PlayThru eliminates the frustration customers often experience with CAPTCHAs.
Fans using the Ticketmaster Apps will be authorized by a 'push' notification in the background during the purchase process that will allow them to bypass the existing type-in CAPTCHA security.
More effective than CAPTCHAs, this lightweight tool is based on proprietary algorithms that detect bot activity in real-time.
We're tremendously excited about this opportunity: we believe that video has the potential to revolutionize Captchas.
The NuCaptcha service currently deploys millions of Captchas a month for a range of enterprise customers.
com, offering a variety of support materials for site owners, including a whitepaper comparison between NuCaptcha and traditional distorted text-based Captchas.
They added tremendous value by coaching us in the intricacies of the business plan competition circuit and guiding us so the judges and potential investors could fully recognize the promise of Are You A Human to remove the significant pains associated with CAPTCHAs.
For brand advertisers, the service creates an advertising platform, enabling them to quickly extend existing campaigns into CAPTCHAs, creating a guaranteed engagement without reproducing any creative assets.
The sluggish response by Everbridge and the City of Boston to this emergency is worse than the response by local, state, and national governments to the damage wrought by Hurricane Katrina, given that it would be very easy for Everbridge to fix this problem or for these cities to procure this service from a company that does not use a visual captcha as the sole means of allowing users to register.
We developed our advertising product a year ago, but insisted on developing a significantly more robust CAPTCHA security platform before offering it to the market: CAPTCHAs are the first line of defense for most sites, and publishers and consumers must be protected," stated Michel Giasson, CEO and Co-Founder of NuCaptcha, Inc.