The Obama administration disclosed this month that for the past year China had access to the confidential records of four million federal employees. This was the biggest breach ever—until the administration later admitted the number of hacked employees is at least 18 million. In congressional testimony last week it became clear the number could reach 32 million—all current and former federal workers.

The Chinese hackers managed to gain “administrator privileges,” allowing them full access to the computers of the U.S. Office...