Microsoft has issued an urgent alert after hackers began exploiting a critical SharePoint Server flaw. The FBI and CISA are responding as agencies and businesses are targeted.

The company said state-backed hacking groups were breaching systems through flaws in SharePoint, which is used by the U.S. government and companies around the world.

Microsoft confirm that Chinese hackers breached its servers, targeting its SharePoint document software and the data of businesses using the platform. The company said the cyberattack was carried out by state-linked “threat actors” who gained unauthorized access to sensitive information stored on the popular collaboration tool.