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.

A sweeping cyber espionage operation targeting Microsoft server software compromised about 100 organizations as of the weekend, two of the organizations that helped uncover the campaign said.

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