The Associated Press reported on Thursday that the White House administration and other government entities are investigating a massive data breach at the U.S. Office of Personnel Management (OPM).

Unknown sources told the AP that approximately the personally identifiable information of four million federal workers  might have been compromised. The breach could impact every federal agency, as OPM serves as the human resources department for the federal government, and it conducts more than 90 percent of federal background investigations.

The breach is thought to have started in May and was detected by the Department of Homeland Security's intrusion detection system, known as EINSTEIN. 

The FBI is also investigating.