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.

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.

Hours after Microsoft revealed hacking groups affiliated with the Chinese government have been exploiting a flaw in its SharePoint software, Bloomberg News reports that the National Nuclear Security Administration has also been breached in the attacks.