An anonymous reader quotes a report from NBC News: The U.S. has issued an emergency warning after Microsoft said it caught China hacking into its mail and calendar server program, called Exchange. The perpetrator, Microsoft said in a blog post, is a hacker group that the company has “high confidence” is working for the Chinese government and primarily spies on American targets. The latest software update for Exchange blocks the hackers, prompting the U.S. Cybersecurity and Infrastructure Security Agency to issue a rare emergency directive that requires all government networks do so.

CISA, the U.S.’s primary defensive cybersecurity agency, rarely exercises its authority to demand the entire U.S. government take protective steps to protect its cybersecurity. The move was necessary, the agency announced, because the Exchange hackers are able “to gain persistent system access.” All government agencies have until noon Friday to download the latest software update. In a separate blog post, Microsoft Vice President Tom Burt wrote that the hackers have recently spied on a wide range of American targets, including disease researchers, law firms and defense contractors. There was no immediate indication that the hack led to significant exploitation of U.S. government computer networks. But the announcement marks the second instance in recent months that the U.S. scrambled to address a widespread hacking campaign believed be the work of foreign government spies.

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