Good and bad CAPTCHAs

December 11, 2007 at 10:16 pm Leave a comment

CAPTCHAs– those distorted letters and numbers that you need to figure out and type in to prove you are human- are everywhere on the Web nowadays. They span the entire spectrum from very bad to competent. The topic of CAPTCHAs also invariably brings forth all the frustrations people have in using them.

Using unsuspecting humans to get around CAPTCHAs is well known. For example, displaying the CAPTCHA from a genuine site to a person to solve in return for the person getting free access to porn.

A blog post on Coding Horror led me to the site of a Chinese hacker that sells software for breaking CAPTCHAs. The site has a very interesting page in which CAPTCHAs from well known sites are shown with how easy (or not) it is to break them. The software price is proportional to the ease of breaking.

For example, 9you (a Chinese online games site) is listed as easy with a 100% cracking rate. On the other hand, cracking eBay CAPTCHAs is listed as moderate with a 70% accuracy rate and is 8 times the price.

Perhaps not so surprising, the three that can’t be broken by the software are Google, Yahoo, and Hotmail. Comments on the Coding Horror page point to Google as having the best CAPTCHA- easy for people to figure out yet impossible to break programmatically.

Score another one for Google!


Entry filed under: authentication, fraud, network, security.

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