A bug discovered in an operating system that runs the majority of the world's computer networks would, if exploited, allow an attacker to bring down the nation's critical infrastructure, a computer security researcher said Wednesday against threat of a lawsuit.

Michael Lynn, a former research analyst with Internet Security Solutions, quit his job at ISS Tuesday morning before disclosing the flaw at Black Hat Briefings, a conference for computer security professionals held annually here.

The security hole in Cisco IOS, the company's "infrastructure operating system" that controls its routers, was patched by Cisco in April, Lynn said, and the flawed version is no longer available for download. But Cisco didn't want the information disclosed until next year when a new version of the operating system would be out of beta testing and ready for distribution.

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