(Washington, DC) -- Accusations of fraud are being hurled by the Justice Department at the government's largest private security background check contractor.

Officials charge former top US Investigations Services executives of a campaign that defrauded the country of millions of dollars. They claim that over a four-year period, more than 660-thousand improper background investigations were turned in.

A civil complaint has been turned in to join a whistleblowers' lawsuit against USIS that's under way in U.S. District Court in Alabama. USIS is defending itself in a statement saying that "Integrity and excellence are core values" at the company.