Audio CAPTCHA easily cracked
Audio CAPTCHA easily cracked
Written by Andrew Johnson   
Friday, 27 May 2011

Many websites rely on CAPTCHA to distinguish genuine humans from bots and malware. Now researchers have devised software that can be trained to decipher and defeat audio CAPTCHAs.


CAPTCHAs are those frustrating tests that ask you to type in characters that correspond to words that have been obscured or defaced by graffiti.

The idea is this task should be easy for humans and impossible for non-humans but to assist the visually impaired many CAPTCHAs offer an audio alternative, in which a computerized voice reads out letters or digits distorted by noise, and these have been proved to be vulnerable to machine recognition.  




Decaptcha is a system to defeat audio CAPTCHAs based on non-continuous speech (i.e. a series of digits or letters rather than spoken words). Devised by a team of computer scientists who presented their research at this week's IEEE Symposium on Security and Privacy in Oakland California, it uses audio-processing techniques to remove the noise and identify the digits.

The software has to be trained, a process that takes around 20 minutes for each type of CAPTCHA, but then can solve CAPTCHAs without human assistance.

The software has proved effective against the systems currently used by eBay (82% accuracy), Microsoft (49%) and Yahoo (45%) but has has much less success with reCAPTCHA which uses background conversations to obscure the digits.

Even so with a success rate of 1.5%, a machine that made hundreds of attempts would quite quickly make a correct match - and would probably have more success than humans who also find reCAPTCHA difficult to decipher.

The researchers conclude that the use of "semantic noise" - i.e. noise such as background conversations or music is the least harmful to human understanding
at levels while also being most able to hinder Decaptcha’s performance.

Full research report:

The Failure of Noise-Based Non-Continuous Audio Captchas



Top 5 Tutorials for the Ajax Enthusiast

Here are five tutorials for getting to grips with Ajax, a technology that allows web pages to be updated asynchronously by exchanging data with a web server behind the scenes. With Ajax, it's possible [ ... ] Five Years On

It is 5 years since first proclaimed its message "Every student in school should have the opportunity to learn to code". Its Hour of Code event has seen exponential growth year [ ... ]

More News

Last Updated ( Saturday, 28 May 2011 )

RSS feed of news items only
I Programmer News
Copyright © 2018 All Rights Reserved.
Joomla! is Free Software released under the GNU/GPL License.