I'm always very vague a first...such as,"in various states," or "midwest," "east and west coast," ect.
some people have left it as that, however, some have gone fishing for a more detailed answer, in which case I spill the beans but remain as vague as possible with it coming off smooth (ideally).
One interviewer persisted until I named all the programs... whatever. I just don't like to lie. All it takes is for them to pick up the phone and check your information. In which case your stooped if they caught you in a lie.