Members of the Department of Government Efficiency uploaded a copy of a crucial Social Security database in June to a vulnerable cloud server, putting the personal information of hundreds of millions of Americans at risk of being leaked or hacked, according to a whistle-blower complaint filed by the Social Security Administration’s chief data officer.

The database contains records of all Social Security numbers issued by the federal government. It includes individuals’ full names, addresses and birth dates, among other details that could be used to steal their identities, making it one of the nation’s most sensitive repositories of personal information.