This paper discusses and demonstrates the interplay between system security and user interface convenience in CAPTCHA design, and in particular, mobile device CAPTCHA design. A CAPTCHA is a computer-based security test used to distinguish human users from artificial users, preventing automated abuse of networked resources. As mobile network services improve, we can anticipate that future mobile...

Online password guessing attacks are a serious threat to the integrity of online accounts. A common defense is ratelimiting, either by slowing down or blocking connections, or by requiring CAPTCHAs to be solved. Either of these options has serious drawbacks, facilitating denial of service attacks, being circumventable by proxies and CAPTCHA solving services, and offering bad usability to the le...

CAPTCHAs have become a very popular security mechanism used to prevent automated abuse of online services intended for humans. Different flavors of CAPTCHA can be seen on Internet. However, a wide variety of CAPTCHAs have been successfully attacked by automated programs. This has made CAPTCHA design an interesting area for research. Among various flavors of CAPTCHA text based are most preferabl...

To distinguish between human user and computer program to enhance security, a popular test called CAPTCHA is used on Web. CAPTCHA has an important role in preventing Denial Of Service (DOS) attacks in computer networks. There are many different types of CAPTCHA in different languages. Due to the expansion of Persian-language and documents on internet, creating a suitable Persian CAPTCHA seems t...

Currently, it is unavoidable of typing CAPTCHA (Completely Automated Public Turing test to tell Computer and Human Apart) before accessing to the Internet. This technique mostly can distinguish bots from human being. Thus, the system is protected from any unwanted persons or programs. There are various researches proposed several of CAPTCHA techniques to protect bots. These are such as Text-bas...

CAPTCHA stands for Completely Automated Public Turing Test to Tell Computer and Human Apart. It is the test that human can pass easily but computer cannot. For example, humans can read distorted text, but current computer programs cannot. For many years, CAPTCHAs have proven very useful for many reputable, Web-based email and application service providers, including social networking sites and ...

We present a black-box attack against an already deployed CAPTCHA that aims to protect a free service delivered using the Internet. This CAPTCHA, referred to as ‘‘Math CAPTCHA’’ or ‘‘QRBGS CAPTCHA’’, requests the user to solve a mathematical problem in order to prove human. We study significant problems both in its design and its implementation, and how those flaws can be used to completely sol...

“CAPTCHA” stands for Completely Automated Public Turing Test[1] to Tell Computers and Humans Apart[2]. Due to exponential growth of internet, security of web application has become a vital issue and many web applications facing a threat of web bots also known as internet Robot is an automated script which executes over the web forms and occupy web spaces and thus increases network traffic. The ...

Accessibility concerns compound the already-considerable difficulties of building systems that provide usable privacy and security. In addition to facing common concerns regarding the semantics of privacy and security tools, people with disabilities face accessibility obstacles, such as the inaccessibility of CAPTCHAs, phishing toolbars, verification images, and other displays that rely upon vi...

Completely automated public turing test to tell computers and humans apart (CAPTCHA) is widely used prevent malicious attacks on various online services. Text- image-CAPTCHAs have shown broader acceptability due usability security factors. However, recent progress in deep learning implies that text-CAPTCHAs can easily be exposed fraudulent attacks. Thus, are getting research attention enhance s...