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 US agency responsible for maintaining and designing the nation’s cache of nuclear weapons was among those breached by a hack of Microsoft Corp.’s SharePoint document management software, according to a person with knowledge of the matter.

Microsoft is issuing an emergency fix to close off a vulnerability in Microsoft’s SharePoint software that hackers have exploited to carry out widespread attacks on businesses and at least some federal agencies.