Threat actors exploit SharePoint flaws to access internal systems, steal sensitive data, and carry out surveillance, impersonation, and extortion.

Microsoft is investigating whether a leak from its early alert system for cybersecurity companies allowed Chinese hackers to exploit flaws in its SharePoint service before they were patched, Bloomberg News reported on Friday.

Microsoft Corp. said a Chinese hacking group is exploiting security vulnerabilities in the company’s SharePoint servers to deploy ransomware, following a cyberattack discovered last week that has affected hundreds of entities around the world.

Hackers sponsored by the Chinese state have breached a number of U.S. government institutions, including the agency responsible for overseeing the security of America’s nuclear arsenal, Microsoft warned.