Here are five notable moments:
“It’s clear now that we didn’t do enough to prevent these tools from being used for harm as well,” Zuckerberg said.
Addressing alleged Russia meddling
Zuckerberg acknowledged Facebook’s slow response to Russia’s alleged covert social media campaign of disinformation and fake news during the 2016 election race.
“One of my greatest regrets in running the company is that we were slow in identifying the Russian information operations in 2016,” Zuckerberg said.
“We expected them to do a number of more traditional cyber-attacks, which we did identify and notify the campaigns that they were trying to hack into them. We were slow in identifying the type of new information operations.”
Later, Zuckerberg hedged on setting higher expectations for the future, conceding that Facebook can do little to prevent foreign actors from using Facebook to meddle in elections.
“As long as there are people sitting in Russia whose job it is to try to interfere with elections around the world, this is going to be an ongoing conflict,” Zuckerberg said.
“This is an ongoing arms race.”
Facebook “working with” Mueller
"I know we're working with them," Zuckerberg said, noting he had to be careful about what he could reveal.
Senator gets personal with Zuckerberg’s privacy
“Mr. Zuckerberg, would you be comfortable sharing with us the name of the hotel you stayed in last night?” Durbin asked. A long pause followed and a wry smile from Zuckerberg preceded a sheepish, “Um, no.”
Durbin then inquired whether Zuckerberg would feel comfortable divulging the names of people he’d messaged in the past week. Zuckerberg, again, said he would not.
“I think that may be what this is all about, your right to privacy,” Durbin then said.
“Your terms of service agreement sucks”
Senators time and again confronted Zuckerberg about Facebook’s user privacy contract, bashing the platform for what lawmakers perceived as a lack of transparency in providing user information to advertisers.
But nobody put a finer point on the matter than Sen. John Kennedy, R-La., who declared, “Your terms of service agreement sucks.”
“The purpose of that user agreement is to cover Facebook's rear end. It's not to inform your users about their rights,” Kennedy said.