This is not a surprise. Simply by putting some information, thoughts or whatever in an email or chat message and sending that to someone else, you lose whatever privacy rights you would've had if you had not shared. In other words, if you want privacy, don't share it. Theoretically, even after the message reaches its destination, a copy of the email or message is likely sitting on a server somewhere and because of that, as far as the DOJ is concerned, it is public information and therefore no warrant is necessary. That's the argument they are using. I think the debate will boil down to what constitutes public information when the data is encoded on a medium that is not the personal property of the sender even if that information is not readily accessible to anyone without expert hacking skills.