One of the advisories also called out a vulnerability in Opera.

The change is part of an expansion of the vulnerability disclosure policy Microsoft launched last summer, said Mike Reavey, the director of the Microsoft Security Response Center (MSRC).

The bugs were discovered by Microsoft researchers, and reported to the security teams responsible for Chrome and Opera. Google patched the two Chrome vulnerabilities last September and December; Opera fixed its browser flaw in October 2010.

The advisories were the first ever from Microsoft for bugs in third-party products. According to Reavey, they will be followed by others, as necessary. "If we're in a situation where we find a vulnerability in some other vendor's product, we will release an advisory ourselves," said Reavey.

At times, those advisories will appear before the affected vendor has a patch ready for users, Reavey acknowledged. "If there's an attack [ongoing], we'll release an advisory, most of the time with workarounds and mitigations, but we will continue to coordinate when we do so," he said.