Zuckerberg later said Facemash and the website that billions of people use today have no relation.
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.
"I've been on Facebook a long time now and all the pictures that I've posted are there and all the things that I've commented on are there and all the blog posts that I've put up were all there".
Mark Zuckerberg's manner has always reminded me of someone, but I could never quite grasp hold of it. About one in three lawmakers got that response over the two days.
Congress gets a visit from planet Zuckerberg. "On Facebook you have control over your information", he said.
"We found that roughly 15 percent of Facebook users polled will decrease in some capacity their use of the platform in light of the Cambridge issue, and we estimate a negligible number of users have deleted their Facebook accounts despite the backlash", Ives says. He gave no further details.
"What we saw at these hearings is that he is resisting changing the business model of Facebook, which is based entirely on harvesting user data and taking that data and use that data to help target ads", David McCabe, a tech reporter with Axios, told Al Jazeera.
Facebook has since shut off the ability of apps to gather such data, but Mr Zuckerberg said it would take "many months" to complete an audit of other apps to determine if they also improperly used data. Since your inception in that Harvard dorm room, many years ago, we've done nothing on Facebook. "Is it true that Facebook is going to charge to use the site?"
In his opening remarks at US Congress, he said: "Facebook is an idealistic and optimistic company".
Whether Facebook tracks offline data through devices that have been connected to Facebook at some point.
Mark Zuckerberg's congressional testimony could have a big effect on the tech leaders of tomorrow. He refrained from cracking jokes and flashed few smiles.
Regulation is certainly one way to catch up on protecting people's data privacy, according to Emily Laidlaw, an associate professor of law at the University of Calgary.
Zuckerberg's testimony will continue when he appears before the House Committee on Energy and Commerce on Wednesday. He did not name specific companies.
Zuckerberg's own representative, Anna Eshoo, Democrat from California asked the CEO: "Do you think you have a moral responsibility to run a platform that protects our democracy?"
What remained as the dust settled on Wednesday was an inability to translate bipartisan concern into regulation due to the complexity of regulating technology issues and the powerful lobbying forces assembled against any effort to do so.
Although much of the current worldwide discussion about internet privacy is focused on Facebook's recently publicized policies and failures, the Gallup poll also found a greater number of Google users are concerned about their protecting their privacy when using the platform-35 percent are "very concerned", a 10-point jump from 2011.