Feeds

Automated crack for Windows Live captcha goes wild

Spammers'Holy Grail

Top 5 reasons to deploy VMware with Tegile

Spammers are using a sophisticated piece of software that can create thousands of Windows Live email addresses by cracking the protections designed to prevent the large-scale creation of fraudulent accounts.

According to security firm Websense, the bot is surreptitiously installed on the PCs of end users. It then establishes a connection to the registration page of the Microsoft-owned mail service. About a third of the time, the software is able to bypass the Captcha requirement through a process that researchers have yet to precisely figure out.

The executable software,has already led to a surge of spam being sent from the Microsoft-owned service, said Dan Hubbard, vice president of security research at Websense. Its discovery comes a few weeks after the release of proof-of-concept code that defeats a similar Captcha used by Yahoo! Mail.

Free email services from Microsoft, Yahoo! and Google are rarely blocked by anti-spam products, making accounts on those services highly prized by spammers. In the past week or so, Websense antispam filters have gone from blocking fewer than 100 Windows Live accounts per day to a number that's in the thousands.

"Some customers were actually flagging the mail as legitimate because it was coming from Microsoft Live," said Hubbard. "Clearly, (spammers) are using the fact that (the services) are legitimate."

Short for "completely automated public Turing test to tell computers and humans apart," Captchas have emerged as a key barrier hindering scammers who want to create large numbers of fake online accounts. In some cases, Captcha-cracking has involved software that transmits the graphic to third-party website that promises a visitor free porn in exchange for typing in the characters. Other times, programs using highly specialized heuristics algorithms try to guess the characters, based on the arrangement of the pixels.

"Captcha breaking has been one of the largest targets of malware operators for some time, even to the point that they will go and farm out the job to human beings," said Adam O'Donnell, a research scientist at antispam company Cloudmark. "It's that profitable."

For years now, the forces of good and evil have been engaged in an arms race of sorts, in which new Captcha cracks beget stronger Captcha images, which in turn lead to more advanced cracks.

Hubbard said a Websense honeynet recently caught malware. When researchers installed it on a lab machine, they discovered that in addition to sending spam, it attempted to create the Windows Live accounts. The software cuts Microsoft's Captcha image and sends it to a server controlled by the scammers. The server then sends the text contained in the image back to the infected PC. The answer is correct as much as 35 per cent of the time.

"We don't know what the process is," said Hubbard. One possibility is that there are human being on the other end, but Hubbard is leaning away from that theory because it would require hundreds of people to make it work. It's also possible the spammers have found a new type of Captcha-cracking software.

Besides being rarely blocked by spam filters, accounts with big email services are valuable to spammers for other reasons. For one, they're free. And for another, the millions of other accounts held by legitimate users makes it hard for the services to pinpoint mass mailers.

Don't count on this cat-and-mouse match ending anytime soon. ®

Remote control for virtualized desktops

More from The Register

next story
Patch NOW! Microsoft slings emergency bug fix at Windows admins
Vulnerability promotes lusers to domain overlords ... oops
Mozilla, EFF, Cisco back free-as-in-FREE-BEER SSL cert authority
Let’s Encrypt to give HTTPS-everywhere a boost in 2015
You really need to do some tech support for Aunty Agnes
Free anti-virus software, expires, stops updating and p0wns the world
Meet OneRNG: a fully-open entropy generator for a paranoid age
Kiwis to seek random investors for crowd-funded randomiser
Got an iPhone or iPad? LOOK OUT for MASQUE-D INTRUDERS
UNjailbroken iOS 7, 8 open to evil, says secbiz FireEye
USB coding anarchy: Consider all sticks licked
Thumb drive design ruled by almighty buck
Attack reveals 81 percent of Tor users but admins call for calm
Cisco Netflow a handy tool for cheapskate attackers
prev story

Whitepapers

Choosing cloud Backup services
Demystify how you can address your data protection needs in your small- to medium-sized business and select the best online backup service to meet your needs.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Simplify SSL certificate management across the enterprise
Simple steps to take control of SSL across the enterprise, and recommendations for a management platform for full visibility and single-point of control for these Certificates.
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.