A CAPTCHA is a Completely Automated Public Test to tell Computers and Humans Apart. Typical CAPTCHAs present a challenge string consisting of a visually distorted sequence of letters and perhaps numbers, which in theory only a human can read. Attackers of CAPTCHAs have two primary points of leverage: Optical Character Recognition (OCR) can identify some characters, while nonuniform probabilitie...

Today’s world revolves around internet technologies. Numerous internet applications and services are available to the users to make life simpler. In this work, we propose to detect and prevent clickjacking attacks by means of establishing a trustworthy map between the user interface and the web application. This is accomplished by the exploitation of agents. There are three agents proposed in t...

This paper studies reverse Turing tests to distinguish humans and computers, called CAPTCHA. Contrary to classical Turing tests, in this case the judge is not a human but a computer. The main purpose of such tests is securing user logins against the dictionary or brute force password guessing, avoiding automated usage of various services, preventing bots from spamming on forums and many others....

CAPTCHAs are a widely deployed mechanism for ensuring that a web site user is a human, and not a software agent. They ought to be relatively easy for a human to solve, but hard for software to interpret. Most CAPTCHAs are visual, and this marginalises users with visual impairments. A variety of audible CAPTCHAs have been trialled but these have not been very successful, largely because they are...

Reverse Turing tests, or CAPTCHAs, have become an ubiquitous defense used to protect open Web resources from being exploited at scale. An effective CAPTCHA resists existing mechanistic software solving, yet can be solved with high probability by a human being. In response, a robust solving ecosystem has emerged, reselling both automated solving technology and realtime human labor to bypass thes...

Smartphones play an important role in the information-communication society and accesses from smartphones to the Internet services increase more and more with the advent of cloud computing. Smartphones have comparatively small displays and it is possible for users to input data through touchscreens. The techniques such as a CAPTCHA (Completely Automated Public Turing test to tell Computers and ...

We propose a new scheme of attack on the Microsoft’s ASIRRA CAPTCHA which represents a significant shortcut to the intended attacking path, as it is not based in any advance in the state of the art on the field of image recognition. After studying the ASIRRA Public Corpus, we conclude that the security margin as stated by their authors seems to be quite optimistic. Then, we analyze which of the...

Existing captcha solutions on the Internet are a major source of user frustration. Game captchas are an interesting and, to date, little-studied approach claiming to make captcha solving a fun activity for the users. One broad form of such captchas – called Dynamic Cognitive Game (DCG) captchas – challenge the user to perform a game-like cognitive task interacting with a series of dynamic image...

A CAPTCHA is a widely used security mechanism to prevent automated access to webpages by malicious users such as internet bots. Introducing elements such as distortion, distracting backgrounds and noise are some ways to make it harder for computer vision algorithms to break them. However, making CAPTCHAs complex by increasing the intensity of these properties has a direct adverse impact on thei...

We explored the relationships between a perceptual-attention task and a word-verification task using event-related potential (ERPs) in preschool children. Adopting an embodied multiple representation perspective, we set up the relationships between online (visual attention) and offline (mental imagery) simulation in the two tasks to test key aspects of abstract word acquisition. Online visualiz...