According to a blog post by a Russian security researcher the CAPTCHA system used by Yahoo! may have been compromised.
Yahoo! CAPTCHA is broken
Few months ago we received information that yahoo CAPTCHA recognition system exists in the wild with the recognition rate about 30%. So we decided to conduct few experiments. We explored yahoo CAPTCHA and designed a similar system with even better recognition rate (about 35%). The vendor was notified. The vendor didn't reply. In this article we’ll present you our own research.
CAPTCHA Security Broken-Get Ready For More Spam
CAPTCHA - Wikipedia, the free encyclopedia
Tools available to beat Yahoo!'s CAPTCHA system | Geek.com
Spam nightmare looms as CAPTCHA is defeated - News - Tech.co.uk
Network Security Research and AI