Be careful what you say on the phone in a crowd of people.
Former National Security Agency director Michael Hayden learned that lesson on a train Thursday.
Hayden gave background interviews to reporters -- meaning he was not to be quoted by name -- but a fellow passenger on an Amtrak Acela train tweeted out his comments to the entire cyber-world.
"Former NSA spy boss Michael Hayden on Acela behind me blabbing 'on background as a former senior admin official,' sounds defensive," tweeted Tom Matzzie, founder of the Ethical Electric Company.
Matzzie, upset at criticisms of President Obama by the former George W. Bush administration official, also tweeted: "Michael Hayden on Acela giving reporters disparaging quotes about admin. 'Remember, just refer as former senior admin.'"
Another entry: "Hayden was bragging about rendition and black sites a minute ago."
Friends of Hayden no doubt alerted him to the broadcast of his background interviews, and he went over to talk to Matzzie.
Matzzie tweeted that out, too.
"I just had a very nice conversation with Michael Hayden," Matzzie wrote. "He was a gentleman and we disagree."