The company says the breach 'has all the markings of a state-sponsored attack.'
U.S. Investigations Services (USIS), which provides background checks for the U.S. government, recently acknowledged that its network was compromised by a cyber attack.
"We are working closely with federal law enforcement authorities and have retailed an independent computer forensics investigations firm to determine the precise nature and extent of any unlawful entry into our network," the company said in a statement. "Experts who have reviewed the facts gathered to date believe it has all the markings of a state-sponsored attack."
DHS spokesman Peter Boogaard told The Hill that some agency employees' information may have been compromised, and that the department has told all employees to monitor their financial accounts for suspicious activity and to watch out for odd requests for personal or financial data.