Some 5 million people hold a government security clearance, according to a 2012 report by the Director of National Intelligence. About 1.4 million people have top-secret clearance, and half of those are the employees of private businesses.
Some 480,000 contractors held top-secret credentials as of last year, and 2,000 companies supply contractors to the intelligence agencies.
Among the largest of those companies is Booz Allen Hamilton, a privately owned consulting company located in Virginia.
The company has deep roots and many connections to the intelligence community.
The current director of national intelligence James Clapper is a former Booz Allen executive. The company's current vice chairman Mike McConnell, was the DNI in the George W Bush administration.
According to the Washington Post, as of 2010, the company contracted more than 23,000 people to the government to do intelligence work at 23 agencies in 15 areas of expertise including technological intelligence, intelligence analysis, and counter intelligence.
The company is estimated to be worth $5 billion annually.