USIS says that their internal security staff detected the breach which, experts say, "...has all the markings of a state-sponsored attack." DHS has suspended all work with USIS since the announcement of the breach.
An unnamed DHS official told Reuters that the Department plans to notify the employees that they may be "impacted" by the breach. Research into the breach continues and more records exposures may be revealed.
If the records contain personal information gathered in background checks it may expose some employees to blackmail.
USIS was in the news last year, having done the background check on Edward Snowden for his government work. At a congressional hearing last June into the Edward Snowden case, the inspector general for the Office of Personnel Management (OPM) told the committee that "we do believe there may be some problems" with the reinvestigation of Snowden in 2011.