I would think that these people who hold these "secrets" would be under a law binding contract that would get them fired from their job immediately
if any of the information got out to the public.
They might even go so far as to threaten them and their family.
There is this guy who lives 3 houses down from me. I hardly ever see him. I know he is there because there is sometimes a very nice Mercedes in the
driveway. He never puts up any christmas decorations, he has blinds on all of his windows, the lights are never on in his house, he always wears a
huge coat, a top hat, and sunglasses when he (rarely) mows his lawn.
IMO the people that work for such organizations have to be so dedicated to it that they would be able to leave their families and social life for
nothing else but the job they are assigned to do. Keeping a secret is just the easy part of the job.