Multiple hacking groups—including state actors from China—have targeted a vulnerability in older, on-premises versions of the file-sharing tool after a flawed attempt to patch it.

Threat actors exploit SharePoint flaws to access internal systems, steal sensitive data, and carry out surveillance, impersonation, and extortion.

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.