Internet Telephony (Voice over Internet Protocol or VoIP) has recently become increasingly popular mainly due to its cost advantages and range of advance services. On the same time, SPam over Internet Telephony (SPIT) referred as unsolicited bulk calls sent via VoIP networks by botnets, is expected to become a serious threat in the near future. Audio CAPTCHA (Completely Automated Public Turing ...

A recent study has found that malicious bots generated nearly a quarter of overall website traffic in 2019 [100]. These perform activities such as price and content scraping, account creation takeover, credit card fraud, denial service, etc. Thus, they represent serious threat to all businesses general, but are especially troublesome for e-commerce, travel financial services. One the most commo...

nerable to protocol-level attacks. For example, a spammer could shift the load of solving Captcha challenges to porn site visitors; a spammer could also outsource such a task to people in countries where cheap labor is available. System design is also important. For example, hackers could bypass some early Captchas simply by reusing a known challenge image's session ID. 3 We have explored anoth...

Internet services designed for human use are being abused by programs. We present a defense against such attacks in the form of a CAPTCHA (completely automatic public Turing test to tell computers and humans apart) that exploits the difference in ability between humans and machines in reading images of text. CAPTCHAs are a special case of ‘human interactive proofs,’ a broad class of security pr...

A CAPTCHA is a special kind of AI hard test to prevent bots from logging into computer systems. We define an AI hard test to be a problem which is intractable for a computer to solve as a matter of general consensus of the AI community. On the Internet, CAPTCHAs are typically used to prevent bots from signing up for illegitimate email accounts or to prevent ticket scalping on e-commerce web sit...

CAPTCHA has been widely deployed by commercial web sites as a security technology for purposes such as anti-spam. A common approach to evaluating the robustness of CAPTCHA is the use of machine learning techniques. Critical to this approach is the acquisition of an adequate set of labeled samples, on which the learning techniques are trained. However, such a sample labeling task is difficult fo...