Computer Literacy Tests

Robot or Human?

CAPTCHA - Pause when you see it; it's one of the rare moments when the invisible war between spammers and programmers becomes visible to you, the prey.


Every Web surfer in the course of his or her browsing, has been forced to stop and perform this weird little task: look at a picture of some wavy, ghostly, distorted letters and type them into a box. Sometimes you flub it and have to re-type the letters, but otherwise, you don’t think about it much. That string of letters has a name; it’s called CAPTCHA. And it’s a test. By correctly transcribing it, you have proved to the computer that you are a human being.

This electronic hoop you have to jump through was invented in 2000 by a team of programmers at Carnegie Mellon University. Somebody at Yahoo! had gone to them, complaining that criminals were taking advantage of Yahoo! Mail-they were using software to automatically create thousands of e-mail accounts, then using those accounts to send out spam. The Carnegie Mellon team came back with the CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart; no the acronym doesn’t really fit) The point of CAPTCHA is that reading those swirly letters is something that computers aren’t very good at. If you can read them, you are probably not a piece of software run by a spammer. Congratulations – you have an e-mail account!!

The CAPTCHA caught on, and now it’s all over the we. Luis von Ahn, as assistant professor at Carnegie Mellon who was part of the original CAPTCHA team, estimates that people fill out close to 200 million CAPTCHAs a day But you should pause when you see one – it’s one the rare moments when the invisible war being waged between spammers and programmers becomes visible to you, the prey. “Of Ciurse,” says Von Ahn, “this has been a little bit of an arms race with spammers, because now there’s a huge incentive for spammers to try to get around CAPTCHAs.” You can bypass them, using brute force, for example, though it will cost you. Go to a website like, you’ll see dozens of ads placed by lots of spammers and other bad actors., who hire whole teams of people to read out and type CAPTCHAs, all day, by hand, by thousands. (How the hell can they manage profit margin?!)

You can also get around CAPTCHAs by being clever. They work only because there are things computers cant do, and there are fewer and fewer of those things all the time. Headlines on tech blogs regularly announce the cracking of CAPTCHAs – Gmail’s, Hotmail’s, Yahoo!’s. Von Ahn doubts the headlines are true – and companies aren’t eager to confirm this kind of rumor – but it’s possible for an amateur, poorly conceived CAPTCHA to be hacked. (A CAPTCHA in which each letter was always formed out of the same number of pixels in a letter to figure out which letter it was looking at)

The faster that software evolves, the harder it gets to distinguish between software and people., the faster CAPTCHAs have to change. They might soon evolve identifying animals or listening to a sound file – anything computers aren’t good at (What’s next?? Tasting Wine? Composing a sonnet?) Von Ahn is confident that the good guys are still ahead for now, but the point at which software can reliably read CAPTCHA in probably as few as three to five years away.

Now what do you think: Will the mail providers be able to survive in this era of spam and malware?? Comment =)

Posted on October 31, 2008, in News. Bookmark the permalink. 1 Comment.

  1. Hardest part is trying to read the frickin’ letters.

    Yes, some CAPTCHAS have an audio option, but sometimes these are broken as it doesn’t spell out the letter that I need.

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