Microsoft is investigating whether a leak from its early alert system for cybersecurity companies allowed Chinese hackers to exploit flaws in its SharePoint service before they were patched, Bloomberg News reported on Friday.

A critical vulnerability in on-premise SharePoint servers allowed state-backed hackers to breach governments and institutions worldwide. Experts are questioning why more hasn't been done or said.

The Department of Energy, which oversees the agency that manages the US nuclear weapons stockpile, confirms it was affected by the SharePoint bug, but says it was 'minimally impacted.'

One of the hacked organizations reportedly includes the U.S. agency responsible for maintaining the country's stockpile of nuclear weapons. China-backed hackers have been observed carrying out the hacks targeting SharePoint servers.

New estimates regarding the recently-exploited Microsoft SharePoint vulnerabilities now evaluate that as many as 400 organizations may have been targeted.

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

Microsoft contained a major SharePoint security flaw, amid fresh questions about the future of its legacy on-premises software.

The name was coined by Dinh Ho Anh, a researcher from Khoa of Viettel Cyber Security, who developed the exploit. The researcher said he picked the name because it exploited ToolPane.aspx, a component for assembling the side panel view in the SharePoint user interface.