Transcript for Facebook CEO Mark Zuckerberg answers questions, addresses possibility of regulation
there. Users actually safe? Is fac being safe? Senator, I Facebooks safe. I use it, mamily use it,ll th people I love and ce about use it all the time. Why should we trust fack to make the necessary change in this. Wve made lot of mistakes. Do you think the average consumer understands what they're signing up for? Don't think the average person likely reads whole document. The fack founder and CEO king hot seat for first time, fac tough questions from over 40 U.S. Senators. On the primaryconcerns, Facebook's growing Rolen our elections. What is Facebook doing to prevent foreign a from inering in U.S. Elections? One ofy top priorit in 2018s to get this right. My my greaterets in ING the company is that we were in identifying the Russian information operations in 2016. We Etem to do Aber more traditional sig attacks, whichid identify and notify the campaigns they wereryg toack into them, we we slow identifying the new type of information operations Reporter: Swapping out his Signe gray t-shirt and jeans for a suit, Zuckerberg ined stoiitting cy for nearly five We've seen thelogy tours before. Your user agreement sucks Reporter: The two D of congressional hearings called as a of that controversial mbanalytica data ea Is keeping track your phone calls and your text messages? Eporter: Many questioning whether thenformation is truly safe on the social nek. Cambridge analy reportedly breached the pros of tens of millions O users -- Repor the millennial billire first arriv in washington ay, meeting pry with lawmakers and dodging questions from report Mr. Zuckerberg, are you doingenough to protect your users Reporter: Twe87 million Facebook users are receg a notice on T feeds informing them their personal data was shared with theiticalsulting firm. Du the hearing, Zuckerberg took personal responsibility for the socnek's failure to safe guard users' privacy. That was a big mistakend it was mytake and I'm sorry. I Ted Facebook, I run it, and I'm responsible fo happens here. I Mark Zuckerberg's going tle lot br tonight than lasnight. He came in sounding well ared, knowledgeable. Certainly O up to his mistakes, which is an important thing to do. Reporter: Zuckerberg admitting face has been used to spread fake news and hate speech. It'ar now that we dtdo enough to prevent these tools omeing usedarm as well. The are great man Americans who I think a D concerned that fac and other tech companies are engaged in pervasive pattef bias and politicacensorship. There hav beenou an with facebo may 2016 gizmoto saidacebook routinelyuppressed nservative stories from ding news, including stories ab Mitt Romney, including stories about glennbeck, to a gr many Americans T appears to be per pattern of pol bs. Do agree with that assessment? Senatoet me say a few things abothis. First, I understand where THA concerns coming from, because Facebook ahh industry are located silicon valley which is extremely left-leaning place. This is actually a con that ve and that I try to root out. The company is making sure that we don't have bias in the work thatdo. And I think it is a fair ncern. There are people Russia whose job its to try T exploit our ems and other internet systd other systems as well. This is a arms race. They're going to Kee on getting better at this, a we need to invest ineeping O getting better at Thi too. Reporter: Last yearook estid that 146 milli Americans russian-linked conturing the election. Lawmakers blasted theompany for not doing more to S it. Ying thatompanies like his had Biven too much lib anee to be regulated. I come in peace. I don't want tote tve to regu Facebook. But bygod, I . Aot of that depenn you. Reporter: Zuckerberg also admihat starting the cnyat such a young a may haveed to its imperfections. It's pretty M impossible, I believ start company in your dormm and then grow it to be at sle that we'ret now without making some mistakes. Eporter: The enteneur was justears old when he and college friends built the first Facebook. Y actions could peently destroy everything I've been working on -- We've beenking on. Reporter: The dramaehind Facebook's developmeigh heated in the academy award-wig film "Theocial network." Not tal about a dating site, I'm talking about taking entiroc experience of college a putting it ne. Rteacebook is now ubiquitous world wide. With M than 2 billion U logging on each nth, sharing everything fromtos to status upda where they work, even the religious and political beliefs. Th that gwing number, there arencing concern a who has access to a user's personal information. One of threats with your data on book is your pho number. It might have been sed by scammers who want T use your information S you or steal your identity. Reporter: Part O the problem may lt in. How do you sustain a buss model I which users don't for Y service? We run ads. Reporter: Facebook makes bi by selling adsased on allhe da they're collecting. In 2017 the company boasted renues of a win$40.7 billion. Earlier this month,facebook chief operating officer, Sheryl Sandberg -- It was infor peo had already listed on fook blicly. Now, that doesn't make -- Reporter: She pointed out that Facebook is free, a suggested users may need to pay to stop Facebook fro collecting and usingheir dat to sell ads. Are you actually considering ha Facebook users pay for you not to use that information? Senator,ple have a control over how their nation is used in ads I the product today. I think whatheryl was saying S that in or to not run ads at all, weould still need some F business model. I actually be willing to pay. I'd like to know, there is a number that you will totally prt my privacy, not use my information for any advertising, any personally targeted stuff all? What's the price? I'd like know that price. Eporter: Concerned, apple cofounder Steve Wozniak announced he's deactivating his facebookcount, joining the "Delete Facebook" movement. Itit breaking point for me. Reporter:ast month it was Facebook in thecrshairs of its data breach. If you areooking at trying to create information weapons, the battle space T you operate I is social media. Ths where the fight pp Rorr: Chris wily worked at Cambridge analytica, a consulting firm which helps political candidates better targetoters online. Wily claims in Sr 2014 Cambridge analytica used a third-party to take data from E faceboo accounts of rough million Americans. Weaponizing the internet Weaponizing the internet, lutely. Reporter: Two years later, Cambridge anica went Ono work for the trump campaign but says it never used that data in question.the campaign itself denies using Cambridge analytica saying it relied on information fromhe RNC. Cambridge analytica has denied wrongdoi Why didn't Facebook ban Cambridge in 2015? Why did you ? Senator, this is clearly one of the questions that I asked our team as as I learned about this, why dide wait until we found out about the reports last month T ban them? Reporter: For those whose data H alrdy been compromised, the breach have far-reaching conseque. Right before Zuckerberg appeared on capitol hill,ebook and Cambridge analytica were hit a class action lawsuit accusing the company of misusin personnformation. It's kelye will stop using Facebook. E social network has become a utility. It not onlys Facebook, it owns Instagram, what's up, and a mber other companies. Reporter:ocial media site says it's doubling down on security, increasing the number mployees working on security from 10,000 to 20,000. Zuckerberg's lm, careful, and rieanor played well. Faok stock increased 4.5%. I think Mark Zuckerberg is comfble being mark Zucker I believacebook is the canary inoal mine. They're the bit, so they're obviously going to get the most scrutiny. The hearing is adjourned. Reporter: For "Nightline," I'm Mary Bruce in Washington.
This transcript has been automatically generated and may not be 100% accurate.