Ads Captcha » inefficient captcha http://adscaptcha.com Mon, 30 Aug 2010 19:42:40 +0000 http://wordpress.org/?v=2.8.1 en hourly 1 PWNtcha – Defeating Captcha http://adscaptcha.com/2009/12/04/pwntcha-%e2%80%93-defeating-captcha/ http://adscaptcha.com/2009/12/04/pwntcha-%e2%80%93-defeating-captcha/#comments Fri, 04 Dec 2009 21:56:55 +0000 Ads Captcha http://adscaptcha.com/?p=80 Captcha, an acronym for “Completely Automated Public Turning Test to tell Computers and Humans Apart“ is a challenge-response test used by websites before user’s registration. This test is mostly based on distorted text with textured background and placed into a small box given at the bottom of the page registration.

The reason websites use Captchas is a strong wish to filter spam sent by spam bots.
Yet weak Captchas can be defeated by PWNTCHA!

What is a PWNTCHA?

Captcha, is a decoder project that decodes Captchas by using visual techniques. It stands for “Pretend We’re Not a Turning Computer but a Human Antagonist” as well as PWN Captchas.

Some Captchas are pretty weak. They consist of one single distorted word and an image, the letters are not rotated or not rotated enough, there is no deformation, or weak deformation, no color variation and weak perturbation. Such Captchas are cracked by PWNTCHA 92% of the time, in a pretty short time (somewhat around 10 seconds! Not more! )

Some harder Captchas, more challenge response tests, consist of 10 words displayed in clutter and distortion and the user is asked to name 3 of them. PWNTCHA succeeds to decode those Captchas 33% of the time.

As a matter of fact PWNTCHA proves the inefficiency of the common Captcha!

Maybe time has come for Captchas to be more difficult for humans as well as computers?…

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