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.

In a blog post Tuesday, Microsoft said it observed hackers attempting to “gain initial access to target organizations.” According to Microsoft, those involved included hacking groups called Linen Typhoon and Violet Typhoon—which Microsoft said are linked to the Chinese government—and China-based group Storm-2603.

US tech giant Microsoft has pointed the finger at China amid a wave of cyberattacks on firms and government agencies worldwide, announcing on Tuesday that it has identified three Chinese hacker groups responsible for the damage so far.