Zuckerberg uncertain of how to answer, stumbled over his words and awkwardly paused before eventually mustering a strong "No" in response.
Due to the time limits for questions, Zuckerberg was unable to elaborate if he personally installed the app himself, or if his data was picked up as part of someone else's account. This lack of understanding points to a broader problem the company has long struggled to address: many of its users are simply not as tech-savvy (or Facebook-savvy) as those behind the social network. More recently, its permission request asks users if they want Facebook to "Continuously upload info about your contacts like phone numbers and nicknames, and your call and text history". I started Facebook, I run it, and, at the end of the day, I am responsible for what happens here.
Though only 270 000 people consented to giving the app their Facebook profile information, the app gained access to 87-million people, including nearly 60 000 South Africans.
"Your right to privacy, the limits of your right to privacy, and how much you give away in modern America in the name of connecting people around the world".
When Graham asked if Zuckerberg thought Facebook was a monopoly, the CEO replied, "It certainly doesn't feel like that to me".
The company pitched its "unique" social media data and "psychographic profiling" to Republican election campaigns.
By the time of the hearing's first break, Facebook's share price had risen by 5% - adding £3bn to his net worth. Americans voice concern over the matter, but fewer than half say it concerns them a great deal.
For all of Zuckerberg's claims that Facebook users own their data, users - and non-users - have no way of determining the full trove of data that the company stores on an individual.
"But it might really be unsettling to people who've had an abortion to have an open debate about that, wouldn't it?"
"Congresswoman", began Zuckerberg - in a tone similar to that of a Best Buy employee explaining to an elderly customer how to restart a computer. "I believe there may be, but I know we're working with them".
Wearing a dark suit and tie instead of his typical T-shirt and jeans, Zuckerberg appeared largely unruffled as senators questioned him.
Many noted that the Facebook boss was living through a lot of people's "worst nightmare" live on TV. "There was the US Senate Alabama special election last year", Zuckerberg added.