When i was taught history in Vietnam, the textbooks mentioned that we captured quite a number of American spies. And our spies were so good that our espionage department at the time played a major role in our later victories. So i am curious to know what is American's side about this matter.
The book "SOG: A Photo History Of The Secret Wars" (ISBN: 978-1581605976) contains an interview by a SOG operator who states that throughout the war, the SEALs and SOG teams were constantly facing higher than usual levels of resistance. They never found out who was compromising them until after the war, when the fellow says that he recognized one of their high level Vietnamese advisors getting a medal on Vietnamese TV. Apparently he'd been dirty the entire time, passing information on special operations to the North Vietnamese Army, and they never figured it out.
My apologies for the vagueness, but I lack physical access to the book at this time. I know there's information in there, though. It's at least the right place to look.