In a blog post Tuesday, Microsoft said it observed hackers attempting to “gain initial access to target organizations.” According to Microsoft, those involved included hacking groups called Linen Typhoon and Violet Typhoon—which Microsoft said are linked to the Chinese government—and China-based group Storm-2603.

Researchers say Chinese actors, along with other criminal hackers, exploited a security flaw in SharePoint software widely used by governments and businesses.

The bugs affecting on-premises builds of SharePoint deployments are officially being exploited by at least two major Chinese nation-state hacking units, the company said. Patches have been issued for all affected versions of SharePoint.