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.

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.

The zero-day vulnerability — which was first disclosed late Saturday — has been exploited by several Chinese state-aligned groups, according to Microsoft.