Chinese hackers breached the U.S. National Nuclear Security Administration through Microsoft SharePoint, with the Energy Department confirming no sensitive information was stolen.

Microsoft has warned that Chinese state-sponsored hackers have breached its SharePoint software used by the US agency responsible for maintaining and modernizing the nation’s stockpile of nuclear weapons, according to a report.

Hackers have breached about 400 government agencies, corporations and other groups, according to estimates from Eye Security, the Dutch cybersecurity company that identified an early wave of the attacks last week.

A series of cyberattacks targeting Microsoft collaboration software, specifically SharePoint, have been linked to Chinese hackers and threat actors.

Microsoft Corp. accused Chinese state-sponsored hackers of using flaws in its SharePoint document management software in a hacking campaign that has targeted businesses and government agencies around the world.

Following criticism of the company’s use of Chinese workers to advise on operation of Department of Defense cloud systems, Microsoft has changed its policy.

The change follows a ProPublica report that outlined how Microsoft’s use of Chinese engineers left U.S. defense clients vulnerable to cybersecurity risks.

Microsoft has relied on engineers based in China for years to help maintain some of the U.S. Department of Defense’s