How CAPTCHA got trashed

CAPTCHA used to be an easy and useful way for Web administrators to authenticate users. Now it's an easy and useful way for malware authors and spammers to do their dirty work.

CAPTCHA — Completely Automated Public Turing Test to Tell Computers and Humans Apart — was a good idea in its day. You presented users with an obfuscated string of characters and then had them decode and type the string in to get an e-mail account, a social networking account or comment access on an online forum. Not much fuss — though users justifiably complained that the difference between '1' (one) and l (the lower-case letter l) can be hard to see in many fonts — and certainly no muss from a Web administrator's point of view.