The largest undercover force the world has ever known is the one created by the Pentagon over the past decade. Some 60,000 people now belong to this secret army, many working under masked identities and in low profile, all part of a broad program called "signature reduction." The force, more than ten times the size of the clandestine elements of the CIA, carries out domestic and foreign assignments, both in military uniforms and under civilian cover, in real life and online, sometimes hiding in private businesses and consultancies, some of them household name companies.