How CAPTCHA got trashed

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 antispam 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 explains. "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.

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. 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," says Chenette. "We've been seeing that quite a lot recently. Of course, search engine poisoning is quite old, but now reputation sites [such as Digg] that use CAPTCHA are being targeted."

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," says Wood. "It's already becoming more difficult for real customers to use them successfully, and they continue to come under increasing pressure from spammers."

Chenette goes further: "CAPTCHA has been broken for the last year and a half. The technology has really not progressed. They've got a little bit harder but the hackers have made programs that can easily break them. This works both with print and audio CAPTCHA. All of these have been broken in one way or the other."

Chenette says it's a "fundamental problem with no simple answer." After all, "harder CAPTCHA solutions mean harder problems for people as well." And he believes that "the idea behind CAPTCHA may need to be part of a solution."

Chenette doesn't expect that a one-size-fits-all solution will emerge, however. "Each site will have to choose its own answer. Financial sector sites, for example, will be more difficult than a free social-networking site," he notes.

Wood expects to see CAPTCHA replaced soon. "I would expect to see some sites introducing new techniques to replace the existing CAPTCHA models, maybe as early as the beginning of next year, perhaps involving 3-D spatial perception, such as the one created by SpamFizzle," he says.
And if that fails in its turn, well, there's always CAPTCHAs like the one used by Quantum Random Bit Generator Service . You do know your math through at least calculus ... right?