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.

At least three China-based hacking teams have been exploiting a previously unknown flaw in Microsoft SharePoint since at least July 7, the company said in a blog post. Why it matters: Microsoft and security researchers didn't uncover the vulnerability until this past weekend,