I thought the following was perhaps the most telling exchange of Zuckerberg's recent testimony before US Senators.

Senator Dick Durbin: Would you be comfortable sharing with us the name of the hotel you stayed in last night?

Mark Zuckerberg: Um... [Long hesitation] No.

Senator Dick Durbin: If you messaged anybody this week, would you share with us the names of the people you've messaged?

Mark Zuckerberg: Senator, no, I would probably not choose to do that publicly here.