Last year, the Department of Homeland Security released a scathing report detailing Microsoft’s mistakes during a 2023 hack in which China stole thousands of emails from top government officials. Two years before that, China-linked cyberattackers compromised more than 250,000 Microsoft Exchange servers.

A program to share information with cybersecurity companies may have exposed unpatched flaws in the company’s SharePoint service.

The company uncovers evidence that at least three China-based hacking groups are abusing the zero-day flaw in SharePoint software to access servers.