Those squiggled words at the bottom of sign-up pages and comment boxes--also known as CAPTCHAs, an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart--are designed to be tough for mere software to decipher, weeding out spambots from humans. Trouble is, humans seem to have a surprisingly tough time cracking them, too.

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The results don't speak well for humans' purported superiority to our robot creations: When the researchers presented the same CAPTCHA to three different humans, they agreed on the right answer only 71% of the time.

For individual humans, CAPTCHA solving accuracy on popular sites was in the ballpark of just 85%. Study participants who were native English speakers successfully deciphered Google's and Yahoo!'s CAPTCHAs 87% of the time, eBay's 93% of the time, and Microsoft's a meager 80% of the time. For ReCAPTCHA, an interesting startup that Google acquired last year, the rate was even lower--just 77%.

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http://blogs.forbes.com/firewall/2010/06/18/those-scrambled-word-tests-for-stopping-spambots-are-tough-for-humans-too/