The ongoing controversy over national security leaks committed by Edward Snowden has drawn attention to his employer, Booz Allen Hamilton, a key government contractor that has employed high-level intelligence officials in Washington.

Like James R. Clapper Jr., director of national intelligence under President Barack Obama. After a long career in the U.S. Air Force, Clapper the years 1995 to 1998 working for Booz Allen as executive director of military intelligence programs.

Booz Allen has become a leading provider of intelligence services to the U.S. government, and along the way picked up veterans of the military like Clapper and others. John McConnell, who was director of national intelligence in George W. Bush’s administration, went through the revolving door in the other direction and now works for Booz Allen, just as he did before he joined the Bush administration. R. James Woolsey, who was the director of the CIA during President Bill Clinton’s first term, went on to spend more than five years at Booz Allen as a vice-president.

Booz Allen Hamilton earns 98% of its revenue from government work, including nearly a quarter of all its revenue (or $1.3 billion) through intelligence work.

“The national security apparatus has been more and more privatized and turned over to contractors,” Danielle Brian, executive director of the Project on Government Oversight, a nonprofit group that studies federal government contracting, told The New York Times. “This is something the public is largely unaware of, how more than a million private contractors are cleared to handle highly sensitive matters.”

Nearly half of Booz Allen’s 25,000-strong workforce has top secret security clearances—which aren’t always approved by actual government employees. Instead, the process of granting security clearances is often handled by contractors for other contractors.