Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

The CAPTCHA Arms Race

Researchers mull the next step in spam deterrents.

Spammers use automated programs called bots to harvest online data, so in 2000, a group of researchers created a bot deterrent called the ­Captcha–the “completely automated public Turing test to tell computers and humans apart.” The first Captchas required people to type in words displayed as images on a Web page in order to access a website.

Mutations: Captchas initially featured familiar words and typefaces but soon evolved into gibberish with distorted backgrounds. Then the words themselves began to warp and in some cases gave way to pictures.

But as bots have gotten smarter and Captchas more complicated, two problems have arisen. The first is that the Captchas can be hard for humans to solve, too. The second is that spammers have simply enlisted networks of humans to attack Captchas.

This story is part of our March/April 2009 Issue
See the rest of the issue
Subscribe

Researchers are tackling both problems. For instance, Jon Bentley of Avaya Labs and Henry Baird, a professor at Lehigh University, have proposed “implicit Captchas” that would present a number of small tests as part of the natural experience of browsing a website. To move from one page to the next, the user might have to click a particular object in an image. Though relatively simple, the tests would be numerous enough to establish that it’s probably a human at the keyboard. But navigating a site would require so much human attention that it wouldn’t be cost effective for spammers to hire networks of Captcha breakers.

Until such new techniques prove themselves in the real world, though, Luis von Ahn, a Carnegie Mellon professor who helped develop Captchas, thinks Web surfers have no choice but to muddle through even difficult ones. “If you got rid of them, all hell would break loose,” he says.

Be the leader your company needs. Implement ethical AI.
Join us at EmTech Digital 2019.

Register now
Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.