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 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,

Microsoft has warned that Chinese state-sponsored hackers have breached its SharePoint software used by the US agency responsible for maintaining and modernizing the nation’s stockpile of nuclear weapons, according to a report.

Victims of the recent global hacking campaign include the National Institutes of Health and the National Nuclear Security Administration, officials said.

Microsoft has issued a stark warning about a recent cyberattack targeting critical infrastructure, including the U.S. National Nuclear Security Administration (NNSA), exposing vulnerabilities in its SharePoint software.

The zero-day vulnerability — which was first disclosed late Saturday — has been exploited by several Chinese state-aligned groups, according to Microsoft.

While the hack doesn't pose the kind of national security threat as the more sophisticated SolarWinds campaign , it can be an existential threat for victims who didn't install the patch in time.