Michael Hayden, director of the spy agency at the centre of the Edward Snowden controversy from 1999 to 2005, was overheard briefing against the Obama Administration to a journalist on a train by a liberal blogger, who proceeded to live tweet his indiscretions.
Tom Matzzie, a one-time occasional blogger for the Huffington Post who now runs a renewable energy company, sat behind Hayden as he spoke to the unnamed journalist "on background" - meaning the reporter was not to cite him by name, instead quoting a "former senior administration official".
Eventually Hayden was alerted to the real-time reporting and towards the end of his micro-blogs Matzzie posted a picture of the two men.
Matzzie chronicled the conversation for his followers, at one point saying: "On Acela listening to former NSA spy boss Michael Hayden give 'off record' interviews. I feel like I'm in the NSA. Except I'm in public."
The Acela Express runs from Washington to New York and Boston. Between Washington and New York it is commonly crammed with political, lobbying and industry heavyweights.
Other tweets included: "Michael Hayden on Acela giving reporters disparaging quotes about admin. Remember, just refer as former senior admin "#exNSAneedsadayjob"
Matzzie later tweeted: "I think I'm safe. Just passed Philly. No rendition yet. Do I have the balls to ask him for a photo? #haydenacela"