Microsoft says China-linked group targets exchange email

Microsoft Corp. is urging customers to download software patches after state-sponsored hackers based in China broke into some customers’ copies of its software for email, contacts and calendar using multiple previously undiscovered flaws.

The attackers used the vulnerabilities to hack into Microsoft Exchange Server, allowing them to break into email accounts and install malware to “facilitate long-term access to victim environments,” Microsoft said Tuesday.

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Microsoft released patches for the flaws in a blog post announcing the attack. “Microsoft has detected multiple 0-day exploits being used to attack on-premises versions of Microsoft Exchange Server in limited and targeted attacks,” the blog said.

Previously undiscovered vulnerabilities are known as zero-days, and they are valuable to hackers because there aren’t defences against them -- at least until they are discovered and patches are created.

“We are sharing this information with our customers and the security community to emphasize the critical nature of these vulnerabilities and the importance of patching all affected systems immediately,” the company said. It added that on-premise systems were affected but the online version of Exchange wasn’t.

The hackers responsible are “a group assessed to be state-sponsored and operating out of China,” according to the blog. They typically target “entities in the United States across a number of industry sectors, including infectious disease researchers, law firms, higher education institutions, defence contractors, policy think tanks, and NGOs.”