This enterprising fellow asked for – and got – a look at the records that DHS has been keeping of his travels:
My biggest surprise was that the Internet Protocol (I.P.) address of the computer used to buy my tickets via a Web agency was noted.
[ . . . ]
The rest of my file contained details about my ticketed itineraries, the amount I paid for tickets, and the airports I passed through overseas. My credit card number was not listed, nor were any hotels I’ve visited. In two cases, the basic identifying information about my traveling companion (whose ticket was part of the same purchase as mine) was included in the file. Perhaps that information was included by mistake.
Some sections of my documents were blacked out by an official. Presumably, this information contains material that is classified because it would reveal the inner workings of law enforcement.
Interesting. If you think so, too, check out the end of the article, which provides easy to follow instructions about filing your own FOIA (Freedom of Information Act) request for your government files. There were a couple of years where it seemed that I was getting SSSS (direction for secondary security) scrawled on my tickets every time I flew, and I’d meant to file a FOIA request to see if there were any clues about that. But then it dropped off, and I forgot about it. I’m curious again.