Except... They aren't only recruiting "smart college grads" they're recruiting smart college Freshmen etc. I know several people who did internships with the NSA/DoD starting their freshmen year. And I can tell you at that point there is still the shiny, "I work for the NSA! This is so cool!" feeling.
How would their friends know you you are working for the NSA? Shurly you sign the official secrets act (the US version of it) at the interview stage and have an agreed cover story for your referees.
