Manager of security research, Websense

Spammers and fraud artists are getting more devious in their efforts to use legitimate services such as Yahoo and Gmail to thwart efforts by Web administrators to prevent bots from opening accounts.

Miscreants are finding ways to get around CAPTCHA, or those ragged, faded, distorted-looking numbers and letters that many Web sites ask users to enter in order to confirm they are real people. CAPTCHA, which stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart, is used by services such as Yahoo, Google, Hotmail and ad site Kijiji.

But there are programs available online that automate CAPTCHA attacks. Moveover, some sites are set up for the sole purpose of getting humans to solve CAPTCHA riddles from other sites, for nefarious purposes.

“The CAPTCHA is presented to a visitor to a pornography site where the pornography is not what this fraudulent person really wants to provide,” said David Senf, director of research for security at IDC Canada in Toronto. “What they’re actually doing is taking this CAPTCHA from a Yahoo account. That’s then pushed off to this individual who’s signing up to this pornographic site (and) keys the CAPTCHA in. The software on the back end pushes it back to Yahoo, signs this computer up to account allows them to use it for another round of spamming.”

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He added fraudsters and spammers are also using optical character recognition software – originally designed to scan hard copies – to solve CAPTCHA quizzes. To counter this, some companies are using more complicated riddles or asking users to identify items on pictures.

“The CAPTCHAS continue to evolve,” Senf said. “You can skew the letters and numbers more. You can obfuscate the background, you can play with the foreground to obfuscate the letters in different ways.”

But there are now programs available online that automate CAPTCHA attacks. You don’t need to have any cracking skills. All you need is a desire to spread spam, make anonymous online attacks against your enemies, propagate malware or, in general, be an online jerk.

Last January, Yahoo Mail’s CAPTCHA had been cracked . Gmail was ripped open in April. Hotmail’s top got popped during the same month.

John Nagle, founder of SiteTruth , a site that tries to identify bogus businesses and their Web sites, wrote in late May on Techdirt that while spam on the popular online classified ad service Craigslist “has been a minor nuisance for years … this year, the spammers started winning and are taking over.”

Craigslist tried “to stop spamming by checking for duplicate submissions,” Nagle explained. “They check for excessive posts from a single IP address. They require users to register with a valid e-mail address. They added a CAPTCHA to stop automated posting tools. And users can flag postings they recognize as spam.”

According to Nagle, waxing sarcastic, “Several commercial products are now available to overcome those little obstacles to bulk posting. A tool called CL Auto Posting Tool is one such product. It not only posts to Craigslist automatically, it has built-in strategies to overcome each Craigslist anti-spam mechanism.”

It’s not the only one. There are, he added, “other desktop software products [such as] AdBomber and Ad Master. For spammers preferring a service-oriented approach, there’s ItsYourPost.” The result? “The defenses of Craigslist have been overrun. Some categories on Craigslist have become over 90 per cent spam. The personals sections were the first to go, then the services categories, and more recently, the job postings.”

Of course, you don’t have to pay anything. There are now free CAPTCHA crackers available online.

Paul Wood, senior analyst at MessageLabs, a U.K.-based e-mail security company, says, “MessageLabs have already begun to see examples of spammers exploiting other techniques once they have bypassed the CAPTCHA of Google and Hotmail — for example, using Google Docs to create spam content and including the link in the spam e-mail messages, evading traditional anti-spam techniques that rely on identifying known spam domains in URLs.”

Social network users are also vulnerable to attack from CAPTCHA-compromised sites, says Stephan Chenette, manager of security research at Websense Security Labs .

“The newer generation doesn’t use e-mail to communicate,” Chenette said. “Instead, they use social networks, and they’re not too concerned about revealing their personal information on social networks or blogs where they post instead of sending e-mail. What happens is that an attacker creates a public blog of his own or sets up an account; he can then use these to publish malicious links. By exploiting the trust of the people on that community, he uses them to spread botnets and the like.”

Because social networks offer such an “enormous attack surface” and “their users don’t think of themselves as being vulnerable in the same way experienced e-mail or IM users are,” they’re especially easy to exploit, says Chenette.

An attacker creates a public blog of his own or sets up an account; he can then use these to publish malicious links. By exploiting the trust of the people on that community, he uses them to spread botnets and the like.Stephan Chenette>Text

Another new attack vector is coming from CAPTCHA’s collapse: the quick creation of fake Web sites. According to Chenette, these sites get their content from legitimate Web sites by copying and pasting to maximize their search engine optimization and reputation to quickly gain an audience.

“Reputation is all the rage for malicious attackers,” Chenette said. “From a search engine perspective, the content is what matters. Malicious attackers will pull sites’ contents and embed it in their site, and that gives them a high search-engine ranking, which gives them a higher reputation.”

So with all these problems, all these new ways to attack users both by e-mail and on social networks and blogs, is there any hope for CAPTCHA?

No, not really.

“I think my view on this now is that time is definitely running out for current CAPTCHA systems; already they are not as effective as they once were,” Wood said. “It’s already becoming more difficult for real customers to use them successfully, and they continue to come under increasing pressure from spammers.”

And even if CAPTCHA systems do get better, they can defeat the Web site’s true purpose, Senf said.

“You just want to buy some tickets (online), you’re up against the clock because you know they’re selling them quickly and you’re trying to type in a darn CAPTCHA that you can’t read. It could be a 4, or is that a P? You’re not sure.”

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