Microsoft blamed two Chinese nation-state actors for exploiting recently discovered security flaws in SharePoint to infiltrate vulnerable organizations, like schools, state governments, and the U.S. government’s top nuclear security agency.

Microsoft released an emergency security patch on Sunday to “mitigate active attacks targeting on-premises servers.”

Patches have been issued for two versions of Microsoft’s SharePoint software, while one version remains vulnerable.

While organizations may have a variety of reasons for sticking with on-premises Microsoft SharePoint servers, widespread attacks targeting the servers are grounds to “re-do their risk calculus” and newly explore cloud-based options,

A newly discovered vulnerability in Microsoft’s SharePoint platform has spurred a mad frenzy from hackers — leading to breaches of some Microsoft clients.

Microsoft warns of active attacks on SharePoint servers used by government and businesses, urging immediate security updates. The FBI is aware and collaborating with partners. A zero-day vulnerability has put tens of thousands of servers at risk,