Mims Bits on MIT‘s Technology Review reports that researchers at UC San Diego have figured out how spammers use low-cost workers in Russia, Southeast Asia, and China to solve millions of CAPTCHAs in near real-time. A CAPTCHA is that bit of distorted text you have to type back at a webpage when you’re trying to sign up for a new email account or leave a blog comment.
In order to prevent spammers from flooding the web with their malware researchers developed CAPTCHAs. CAPTCHAs are designed to be easy for humans to solve but challenging enough for computers to get right that automated systems would not be effective.
In what Mims calls an epic new analysis by the UC San Diego researchers, they uncovered the “seedy underbelly” of a sophisticated, highly automated, worldwide network of services that help spammers get past the CAPTCHAs. The article says that the inventors of CAPTCHA probably didn’t expect thousands of laborers working for less than $50 a month would be recruited by spammers to solve an endless stream of CAPTCHAs. Automated middlemen deliver the CAPTCHAs to the workers and then sell the results to spammers in real-time so that their spambots can use those solutions to post to blogs and set up fraudulent email accounts according to a paper (PDF) delivered at the USENIX Security 10 Symposium.
The UC San Diego researchers analyzed where the workers involved in this scheme were located and found that they are based in India, Russia, Southeast Asia, and China. The system is so efficient at delivering CAPTCHAs to workers in these remote locales that the average time for delivery of a solution hovers around 20 seconds. ImageToText, one of the CAPTCHA services the researchers experimented with was able to deliver correct results in “a remarkable range of languages,” including Dutch, Korean, Vietnamese, Greek, and Arabic.
Even setting the sample CAPTCHAs to Klingon, as a control in their experiment, could not stop ImageToText, according to Technology Review. The workers managed to solve a handful of the Klingon CAPTCHAs despite odds of less than one in one thousand of their randomly getting the right answer.
The results of this landmark study, says Mims, show that a number of sites, including those run by Microsoft (MSFT), AOL, Google (GOOG), and the widely used reCAPTCHA, are regularly compromised by spammers employing these services. The researchers conclude that their investigation with an anonymous “Mr. E” who actually runs one of these services, proves that for advanced spammers, CAPTCHAs aren’t so much a barrier as a cost of doing business.
DarkReading has a report that independent security researcher Chad Houck recently demonstrated his work on solving Google’s reCAPTCHA. reCAPTCHA was designed to stop software bots attempts to create free accounts on the Google services for their malware ways. Despite recent enhancements made by Google, DarkReading says Houck came up with algorithms that could beat reCAPTCHA 30 percent of the time.
A 30% success rate means that automated software using Mr. Houck’s algorithm will be able to create one Google account out of just three attempts. Multiply those odds by the endless attempts by tens of thousands of zombies in a typical botnet, reCAPTCHA is broken.
In the DarkReading article, Houck notes that “[ReCAPTCHA] has never been wholly secure. There are always ways to crack it.” The researcher has since published a white paper on it, and has also released his algorithms online. For now, at least, a Google spokesperson says there has not been any sign of this particular attack being actively used.
Related articles
- Why reCAPTCHAs Are Actually A Good Thing (levynewsnetwork.wordpress.com)
Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.
– Updated 03-19-2011 – After the recent discovery of some 50+ malicious applications on the official 
