22 COPublished by the ieee COmPuter and reliability sOCieties ■ 1540-7993/09/$26.00 © 2009 ieee ■ July/august 2009 Completely Automated Public Turing Tests to Tell Computers and Humans Apart (CAPTCHAs) are now an almost standard security mechanisms for defending against undesirable and malicious bot programs on the Internet (especially those bots that can sign up for thousands of accounts a min...

The advent of electronic voting gives rise to a new threat: Adversaries may execute undetectable, automated attacks against the system. Elections are often secured through complex policies, which may be difficult to enforce; Completely Automated Public Turing Tests to Tell Computers and Humans Apart (CAPTCHAs) provide an inexpensive alternative. The goal of this study is to introduce a unique a...

In this paper, we develop some new Captchas belonging to genre — “CAPTCHAs with a purpose.” These CAPTCHAs apart from having its applications serve some useful purpose. reCAPTCHA is one such Captcha developed at Carnegie Mellon University. It helps to digitize books. Another such Captcha is Asirra developed at Microsoft which provides homes for homeless animals. In this paper, we present Time b...

A CAPTCHA is a challenge-response test often used on the Web to determine whether a Web site’s visitor is a human or an automated program (so called bot). Existing and widely used CAPTCHA schemes are based on visual puzzles that are hard to solve on mobile devices with a limited screen. We propose to leverage movement data from hardware sensors to build a CAPTCHA scheme suitable for mobile devi...

A CAPTCHA is a program that allows or denies access to services by generating and grading test that humans can pass but current computer programs cannot. Captchas are generally used to protect free web services from automated programs. Also, they can provide an idea of which fields in artificial intelligence are the most explored and which could be researched in the near future. Most of the tes...

Existing CAPTCHA solutions are a major source of user frustration on the Internet today, frequently forcing companies to lose customers and business. Game CAPTCHAs are a promising approach which may make CAPTCHA solving a fun activity for the user. One category of such CAPTCHAs – called Dynamic Cognitive Game (DCG) CAPTCHA – challenges the user to perform a game-like cognitive (or recognition) ...

CAPTCHA is widely used security technique employed to avoid automated form submissions or verify user as human. An alternative CAPTCHA method based on pattern matching and number recognition ability is proposed in this paper, which verifies user as human and prevents bots to intervene and spam applications or services. This method is based on user gestures which make it unique and secure. The b...