Researchers at Stanford University recently found that 13 out of 15 CAPTCHA methods from leading Web sites were vulnerable to automated attacks.

"Their techniques including removing deliberately introduced image background noise and breaking text strings into single characters for easier recognition," writes The Register's John Leyden. "The team built an automated tool, called Decaptcha, that applied these various tricks."

"In a research paper [PDF file], the Stanford team suggest several approaches towards making CAPTCHAs harder to beat, including making the length of a text string changeable and randomising character font and size," Leyden writes.

Go to "Report: Popular CAPTCHAs easily defeated" to read the details.

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