"A security researcher has claimed that Yahoo’s system for blocking automated access to its systems – the CAPTCHA image-recognition system – has been effectively cracked. CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) systems are used by Yahoo, as well as Google, Microsoft and others, to stop automated systems from registering web-based email accounts, filling blog comments sections with spam and guessing passwords.
The systems typically present users with a series of characters that can be deciphered by humans, but not by image-recognition software. Various implementations of automated CAPTCHA-cracking software have been developed, largely by spammers, but Yahoo’s CAPTCHA system so far has been ranked as one of the toughest to crack." – Content courtesy of Researcher cracks Yahoo CAPTCHA software