A new report by security researchers claims that Google’s reCAPTCHA system is flawed – so flawed that it would allow a botnet with just 10,000 zombies to manage 10 recognition successes an hour resulting in over 850,000 fake accounts being registered each day. The researchers say the flaw is the same one that has plagued all CAPTCHA services -the human factor- but with a twist.

The Koobface botnet is distributing a new variant of its Trojan that forces the user of the computer it infects to solve a CAPTCHA. The user is presented with a Windows pop up directing them to solve the CAPTCHA provided or their system will be shut down. The solved CAPTCHA is then sent to the botnets C&C channel and used to create a fake Blogspot blog which is populated with content from Google News. Koobface uses SEO techniques to insure these blogs are packed with hot topics and sure to appear at the top of search engines. The links in these fake blogs redirect to a fake Facebook page where the user is directed to download a “flash player update” which is really the Koobface Trojan. The same technique is used to create fake Gmail and Facebook accounts which are also used to distribute the malware. Once Koobface infects a system it steals credit card numbers and other personal information.

The underground economy of human driven CAPTCHA solving is booming as well, further weakening the effectiveness of CAPTCHA systems. Services offering bulk orders of solved CAPTCHAs for Web 2.0 and social media services are exploding and prices are lower than ever. One service offers 1 million solved CAPTCHAs for $800. However, with Koobface taking CAPTCHA solving into its own hands, other malware distributors may follow suit, leading to the CAPTCHA solving industry’s demise.

Google denies that their reCAPTCHA is flawed, claiming the data used in the report is outdated.

           “Therefore, this study does not reflect the effectiveness of reCAPTCHA’s current technology against machine solvers,” said a Google spokesman. “We’ve found reCAPTCHA to be far more resilient while also striking a good balance with human usability, and we’ve received very positive feedback from customers.”