Feeds

(New) dirt-cheap bots attack Hotmail Captchas

Captcha catching grows up

3 Big data security analytics techniques

UK researchers have devised a novel and inexpensive way of cracking Microsoft's Windows Live Captchas with a success rate of more than 60 percent, a finding that further exposes weaknesses in a key measure designed to keep miscreants from infiltrating free online services.

In a paper (PDF) published Monday, Jeff Yan and Ahmad Salah El Ahmad, of the School of Computing Science at Newcastle University, lay out a way to crack the Captcha used to protect Windows Live Hotmail. Using custom-written software, a standard desktop computer was able to correctly read the characters more than 60 percent of the time. Microsoft designed it with the goal that automatic scripts should not be more successful than 0.01 percent of the time.

The paper follows research released last week by Websense Security Labs that tracked automated bots in the wild that were creating random Hotmail accounts after cracking the Captcha.

While attacks on Captchas deployed by Microsoft, Google and Yahoo are nothing new, the latest research appears to show new strides in the breaking of such protections. Short for "completely automated public Turing test," a way of distinguishing between computers and humans, most Captchas require end users to identify the letters depicted in a highly distorted image designed to be unreadable by computer scanners.

In many of the previous attacks - for instance, one against Hotmail that was observed by Websense in February - it was unclear if there was cheap human labor that was reading the Captcha images, and in any event, the scripts were successful no more than 35 percent of the time. Websense observed similar attacks on Gmail that succeed only about 20 percent of the time. A Google software engineer contends the attacks are being carried out in Russian sweatshops.

In January, researchers reported successfully cracking Yahoo's Captcha. According to Yan, Yahoo updated its Captcha last month to make it more resistant to attack.

The Newcastle researchers took a decidedly different approach. They figured out a way to isolate each of the eight characters that make up a Hotmail Captcha image. Defeating Microsoft's so-called segmentation-resistant technology was a major accomplishment. It blends the characters together in an attempt to thwart optical character recognition. Once they were able to segment the image - usually in about 80 milliseconds using a PC with a Core 2 and 2 GB of random access memory - the machine could easily read the individual characters.

"For the first time, we have shown that although Microsoft's MSN Captcha intentionally bases its robustness on segmentation resistance, it is vulnerable to a simple, low-cost segmentation attack," the researchers wrote. "Therefore, our work shows that the MSN scheme provides only a false sense of security."

The latest attack observed by Websense seems to make similar strides. Scripts obtained by company researchers were able to successfully respond a Captcha challenge in about six seconds, leading them to deduce that the recognition is happening automatically, rather than relying on a human being.

"We don't know exactly how the MSN one is done," said Dan Hubbard, vice president of security research at Websense. "They're getting quite a bit more automated."

What we do know is that up until now Captchas have been an important defense in the never-ending battle against spam. Already, anti-spam services have begun throttling messages sent from Gmail and Yahoo in response to the growing abuse of such services. If you think the spam epidemic is bad now, just wait until these new cracks go mainstream. ®

3 Big data security analytics techniques

More from The Register

next story
Obama allows NSA to exploit 0-days: report
If the spooks say they need it, they get it
Samsung Galaxy S5 fingerprint scanner hacked in just 4 DAYS
Sammy's newbie cooked slower than iPhone, also costs more to build
Putin tells Snowden: Russia conducts no US-style mass surveillance
Gov't is too broke for that, Russian prez says
Snowden-inspired crypto-email service Lavaboom launches
German service pays tribute to Lavabit
Mounties always get their man: Heartbleed 'hacker', 19, CUFFED
Canadian teen accused of raiding tax computers using OpenSSL bug
One year on: diplomatic fail as Chinese APT gangs get back to work
Mandiant says past 12 months shows Beijing won't call off its hackers
Call of Duty 'fragged using OpenSSL's Heartbleed exploit'
So it begins ... or maybe not, says one analyst
Heartbleed exploit, inoculation, both released
File under 'this is going to hurt you more than it hurts me'
prev story

Whitepapers

Securing web applications made simple and scalable
In this whitepaper learn how automated security testing can provide a simple and scalable way to protect your web applications.
3 Big data security analytics techniques
Applying these Big Data security analytics techniques can help you make your business safer by detecting attacks early, before significant damage is done.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Top three mobile application threats
Learn about three of the top mobile application security threats facing businesses today and recommendations on how to mitigate the risk.
Combat fraud and increase customer satisfaction
Based on their experience using HP ArcSight Enterprise Security Manager for IT security operations, Finansbank moved to HP ArcSight ESM for fraud management.