PC World reports that an accidental leak may have confirmed Chinese hackers' suspicions that Internet Explorer has a critical unpatched vulnerability, a security researcher said.

The bug was one of about 100 found by noted browser vulnerability researcher and Google security engineer Michal Zalewski using a new "fuzzing" tool. The vulnerabilities were in IE, Firefox, Chrome, Safari and Opera.

"I have reasons to believe that the evidently exploitable vulnerability [in IE] discoverable by cross_fuzz is independently known to third parties in China," said Zalewski, referring to the "cross_fuzz" fuzzing utility he created.

  Chinese Hackers Dig Into New IE Bug, Says Google Researcher