WASHINGTON (CBSNewYork/AP) — Facebook CEO Mark Zuckerberg testified before a House committee Wednesday, his second day of grilling by lawmakers over concerns about users’ privacy.

In his opening statement to the House Energy and Commerce Committee, Zuckerberg said “it’s clear now that we didn’t know enough to prevent these tools from being used for harm as well.”

“We didn’t take a broad enough view of our responsibility and that was a big mistake. It was my mistake and I’m sorry,” he said.

Zuckerberg House Committee Testimony Part 1: 

Zuckerberg House Committee Testimony Part 2: 

Zuckerberg House Committee Testimony Part 3: 

Facebook has said that 87 million people’s personal data was scooped up when some 270,000 users took a personality quiz and had not just their data, but the data of their friends to be accessed by an outside app. Cambridge Analytica then obtained this data and is said to have used it to try to influence elections around the world.

Answering a question from Rep. Anna Eshoo, a Democrat from California, Zuckerberg acknowledged his own personal data was included in the personal information sold to malicious third parties.

When he was asked if he is willing to change his business model in the interest of protecting personal privacy, he said “I’m not sure what that means.”

When Eshoo asked if he thinks he has a moral responsibility to run a platform that protects our democracy, Zuckerberg answered, “yes.”

Zuckerberg also said Wednesday he believes it is “inevitable that there will be some sort of regulation” of his industry but warned lawmakers to be careful about what they propose.

“The internet is growing in importance around the world in people’s lives and I think that it is inevitable that there will need to be some regulation,” Zuckerberg said. “So my position is not that there should be no regulation but I also think that you have to be careful about regulation you put in place.”

Larger, more dominant companies like Facebook have the resources to comply with government regulation, he said, but “that might be more difficult for a smaller startup to comply with.”

New Jersey Democratic Rep. Frank Pallone asked if Facebook limits the amount of data that is being shared.

“Congressman, yes,” Zuckerberg said. “In response to this issue, we’ve changed a lot.”

Zuckerberg also said Facebook doesn’t sell data to advertisers.

“Advertisers don’t get access to your data,” he said. “There is a core misunderstanding about how that system works.”

In a response to a question from Republican Rep. Pete Olson of Texas about data security, Zuckerberg said the “sheer volume of content on Facebook” makes it so that “no amount of people we can hire will be enough to review all of the content.”

Zuckerberg noted the need for building new AI tools to help the company monitor content, including fake accounts, CBS News reported.

On Tuesday, Zuckerberg took questions from 44 senators and said they learned in 2015 that Cambridge Analytica had bought data from the app developer on Facebook.

“We took down the app and we demanded that both the app developer and Cambridge Analytica delete and stop using any data that they had,” he said Tuesday. “They told us that they did this. In retrospect, it was clearly a mistake to believe them.”

He admitted the company has not done enough to protect users’ personal information.

“We didn’t take a broad enough view of our responsibility and that was a big mistake,” he said. “It was my mistake and I’m sorry.”

But many of the senators were skeptical.

“We’ve seen the apology tours before,” said Democratic Conn. Sen. Richard Blumenthal.

Republican Sen. John Thune of South Dakota said Zuckerberg’s company had a 14-year history of apologizing for “ill-advised decisions” related to user privacy.

“After more than a decade of promises to do better, how is today’s apology different?” Thune said.

“We have made a lot of mistakes in running the company,” Zuckerberg conceded, and Facebook must work harder at ensuring the tools it creates are used in “good and healthy” ways.

Zuckerberg said Facebook itself will work to notify users and prevent future breaches of privacy.

“It will take some time to work through all the changes we need to make across the company, but I’m committed to getting this right,” said Zuckerberg.

The senators asked Zuckerberg how he’d feel if his personal information was compromised.

“Would you be comfortable sharing with us the name of the hotel you stayed in last night?” said Sen. Dick Durbin.

“Um, no,” Zukerberg replied.

Zuckerberg also said his company is “working with” special counsel Robert Mueller in his probe into Russian interference.

Earlier this year Mueller charged 13 Russian individuals and three Russian companies in a plot to interfere in the 2016 presidential election through a social media propaganda effort that included online ad purchases using U.S. aliases and politicking on U.S. soil. Some of the Russian ads were on Facebook.

Zuckerberg said he has not been personally interviewed and said he is not aware if the company has been subpoenaed.

But the concern now is Russia using social media to meddle in upcoming elections. The 33-year-old Zuckerberg is vowing that the company is now investigating all apps and says the company will do a better job at regulating access to data.

“This is an ongoing arms race,” he said. “They’re going to keep on getting better at this and we need to keep investing on getting better at this too.”

Facebook had lost about $100 billion in value since February. The company’s stock surged more than 4 percent during Zuckerberg’s testimony on Tuesday.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)