It happened to me. I was flying out of San Francisco once on an international flight.
And at SFO some of the international terminals go through these long corridors to connect to that moveable tunnel that connects to a plane.
I was fixing some bug on my laptop and decided to wait till the last minute to board (though I was sitting right infront of the check-in desk).
When I went past the check-in desk and into the corridor, two police officers approached me and asked me if they could ask a few questions.
It felt suspicious right away why they were stopping me as there were hardly any people around - there was no one behind me, and everyone had already gone through the corridor.
They took me aside into a small room and asked me where I was travelling to and for what purpose. But then they repeated
a number of times that it's illegal to carry more than $10,000 in cash and if I was carrying over that amount and that if I was it would have to be confiscated.
I told them I wasn't and I think I only had less than $500 in my wallet. They went through my wallet, went through my bag pack, even flipped
through my Clojure book and then they let me go. But I kept having that feeling that something didn't feel right. Later I wished I had asked for the officers names or if that would have gotten me into trouble with them.