Facebook CEO Mark Zuckerberg was calm throughout his hearing, answering questions candidly and confidently. But there was one question that caught him off guard.

The question came from Senator Dick Durbin, who simply asked: "Mr Zuckerberg, would you be comfortable sharing with us the name of the hotel you stayed in last night?"

Zuckerberg uncertain of how to answer, stumbled over her words and awkwardly paused before eventually mustering a strong "No" in response.

Durbin wasn't done with him yet and followed this up with another spiky question.

"If you've messaged anyone this week, would you share with us the names of the people you've messaged," the Senator asked Zuckerberg.

Having now committed to his stance, Zuckerberg this time responded with a little more poise, saying, "Senator, no, I would probably not choose to do that publicly here."

While the question didn't focus on Cambridge Analytica or the Russian probe it got to the heart of what the data debate is really about: the right of a person to keep certain information private.

During the questioning, Zuckerberg said that users consent to Facebook's data policy not only when agreeing to the terms of service but also when agreeing to share information with apps or other users.

Numerous Senators on the panel did, however, question whether users were giving informed consent; in other words, whether they knew what they were agreeing to.

As senator Kamala Harris explained: "Your user agreement sucks. You can spot me 75 IQ points. If I can figure it out, you can figure it out. The purpose of the user agreement is to cover Facebook's rear end. It is not to inform your users about their rights. You know that and I know that. I am going to suggest to you that you go back home and rewrite it."