"But while no one has yet come up with a computer that can fool
people into thinking it's another person, computers are great at
fooling other computers. These days, malware makers and spammers
regularly trick the CAPTCHA systems at big-name Web sites such as
Yahoo Mail, Gmail and Craigslist, and use these sites to automate
their attacks. So what can we do? Can CAPTCHA be saved?...
"Unfortunately, beginning in early 2008, crackers started
getting the better of the CAPTCHA systems. In short order, Yahoo
Mail's, Gmail's and Hotmail's CAPTCHA defenses were cracked.
"Then, adding insult to injury, the crackers started releasing
their work in the form of do-it-yourself CAPTCHA cracking software
that anyone could use. For example, a program called CL Auto
Posting Tool attempts to post bogus ads to Craigslist while
automatically overcoming Craigslist's antispam protections."