Facebook CEO Mark Zuckerberg testified before Congress for the first time Tuesday. (Screenshot via C-SPAN)

Facebook CEO Mark Zuckerberg spent hours in the hot seat Tuesday, answering questions from a joint hearing of the U.S. Senate’s Judiciary and Commerce Committees. But unlike the brutal grilling some anticipated, the questions were mostly exploratory, signaling that there is much our lawmakers still don’t understand about the most powerful social network ever built.

The hearing focused on the Cambridge Analytica scandal, in which a Republican-backed political strategy firm accessed data from up to 87 million unwitting Facebook users. Zuckerberg was also asked about the role Facebook played in attempts by the Russian government to interfere in the 2016 presidential election. Read Zuckerberg’s prepared testimony here.

Wall Street responded positively on Tuesday, as shares were up more than 4 percent. Facebook’s market capitalization dropped by $100 billion between Feb. 2 to March 29.

Continue reading for 5 key takeaways from Zuckerberg’s testimony Tuesday.

1. Facebook is working with Special Counsel Robert Mueller for the Russian election meddling investigation

Sen. Patrick Leahy (D-VT) told Zuckerberg he assumes “Facebook has been served subpoenas from Special Counsel Mueller’s office,” to which Zuckerberg initially answered, “yes” but later clarified that “I am actually not aware of a subpoena.” Zuckerberg said he has not been interviewed himself but others on his team have.

“I want to be careful here because our work with the special counsel is confidential and I want to make sure that in an open session I’m not revealing something that’s confidential,” Zuckerberg said.

2. Zuckerberg believes Facebook is more trustworthy with data than government

In a discussion about how law enforcement agencies handle personal information, Sen. Dean Heller (R-NV) asked Zuckerberg if he believed Facebook was “more responsible with millions of Americans’ personal data than the federal government would be.”

After a pregnant pause, Zuckerberg answered, “yes.” But he went on to explain that Heller’s comparison is poor because government surveillance is done without consent. Zuckerberg said users on Facebook consent to share the data they post on the social network.

3. Facebook may be considering a premium option

Zuckerberg hinted that a paid version of Facebook could be in the works. Sen. Orrin Hatch (R-UT) recalled Zuckerberg’s first visit to Washington, D.C. back in 2010.

“You said back then that Facebook would always be free,” Hatch said. “Is that still your objective?”

“Yes,” Zuckerberg said. But tellingly, he added “There will always be a version of Facebook that is free.”

That suggests that a premium version is not out of the question. A paid option could help Facebook reduce its reliance on third-party advertisers, a relationship that is responsible for many of the company’s current headaches.

4. On competition

In a series of questions, Sen. Linsdey Graham (R-SC) pressed Zuckerberg to reveal who Facebook’s chief competitor is. Zuckerberg said segments of his business compete with various companies but declined to name just one.

“You don’t think you have a monopoly?” Graham asked.

“It certainly doesn’t feel like that to me,” Zuckerberg answered.

5. On privacy

In an exchange that got to the heart of the privacy issues Facebook is grappling with today, Sen. Dick Durbin (IL) asked Zuckerberg, “would you be comfortable sharing with us the name of the hotel you stayed in last night?”

Zuckerberg laughed, thought about it, and answered, “Uh, no.”

“If you messaged anybody this week, would you share with us the names of the people you’ve messaged?” Durbin asked.

“Senator, no,” Zuckerberg said. “I would probably not choose to do that publicly here.”

That, Durbin said, is “what this is all about.”

“Your right to privacy,” he went on. “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.’ The question is what information Facebook’s collecting, who they’re sending it to, and whether they’ve asked me in advance, my permission to do that. Is that a fair thing for a user of Facebook to expect?”

“Yes, Senator,” Zuckerberg said. “I think everyone should have control over how their information is used.”

Some other highlights from the hearing on Tuesday:

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