In the episode "The woman in the car" a one-time character, agent Pickering from the state department, is interviewing the employees at that branch of the Jeffersonian, with mostly humorous responses.
When she interviews Brennan, she asks about her relations with a Cuban national. Brennan gets on the phone, calls someone from the state department, and the investigation is suspended immediately, implying that Brennan has very high security clearance that includes some sensitive information, sensitive enough to have all of agent Pickering's notes destroyed.
Was Brennan's very-high security clearance ever explored in a later episode? I've seen most of them, but missed a few of the last couple seasons. I'm just curious if her clearance was every explored in more detail in a later episode. I googled "Temperance Brennan security clearance" and all the references are to this episode only, so I'm thinking it was a one-off, but if anyone can point out any other episodes where it came up I'd be grateful.