A critical flaw in Sendmail, the Internet's most popular email server, has become the first test for the US' newly minted Department of Homeland Security and its cyberdefence arm.

The DHS's Directorate of Information Analysis and Infrastructure Protection (IAIP) worked with security company Internet Security Systems, which discovered the flaw, and Sendmail to create a patch while keeping news of the issue from leaking to those who might exploit the vulnerability.

"Working with the private sector, we alerted key owners of the vulnerable software and got them talking," said David Wray, spokesman for the IAIP Directorate. "We think this is a great example of how this should, and does, work."

The Department of Homeland Security got high marks from the security community for giving companies the necessary time to create the patch and for synchronising its release.

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