U.S. National Nuclear Security Administration was among those breached by a hack of Microsoft's SharePoint document management software, Bloomberg News reported on Tuesday, citing a person with knowledge of the matter.

While Microsoft has patched its software in recent days, cybersecurity researchers have already detected breaches on more than 100 servers representing 60 victims thus far

Microsoft said it identified 2 groups as leveraging flaws in SharePoint software; China said it firmly opposes all forms of cyberattacks.