Microsoft has issued an alert about “active attacks” on server software used by government agencies and businesses to share documents within organizations, and recommended security updates that customers should apply immediately.

Hackers sponsored by the Chinese state have breached a number of U.S. government institutions, including the agency responsible for overseeing the security of America’s nuclear arsenal, Microsoft warned.

A critical flaw in a major Microsoft document storage tool is hitting the organizations least able to defend themselves, security researchers and incident responders tell Axios. Why it matters: Schools,