Despite denials from Google, a security researcher continues to assert
that the Search King's reCAPTCHA system for protecting Web sites from
spammers can be successfully exploited by Internet junk mail panderers.
Researcher Jonathan Wilkins
published a paper recently that included an analysis of reCAPTCHA's
security. In automated attacks he conducted against the system, he
reported he had an alarming success rate of 17.5 percent.
Download the Wilkins document: