An investigation is underway after hackers used a security flaw in Microsoft software to internationally infiltrate agencies and businesses over the weekend.

Microsoft said in a post on its website on Saturday that it was “aware of active attacks targeting on-premises SharePoint Server customers by exploiting vulnerabilities.” SharePoint is a Microsoft platform that allows customers to manage and share documents within their organizations.

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