Facebook says the personal information of up to 87 million users, mostly in the US, may have been improperly shared with political consultancy Cambridge Analytica, up from a previous news media estimate of more than 50 million.
Chief Executive Mark Zuckerberg said in a conference call with reporters on Wednesday that Facebook had not seen "any meaningful impact" on usage or ad sales since the scandal, although he added, "it's not good" if people are unhappy with the company.
Zuckerberg told reporters he accepted blame for the data leak, which has angered users, advertisers and lawmakers, while also saying he was still the right person to head the company he founded.
"When you're building something like Facebook that is unprecedented in the world, there are going to be things that you mess up," Zuckerberg said, adding that the important thing was to learn from mistakes.
He said he was not aware of any discussions on the Facebook board about him stepping down, although directors would face a challenge if they wanted to oust him because Zuckerberg is the controlling shareholder.
He said he had not fired anyone over the scandal and did not plan to. "I'm not looking to throw anyone else under the bus for mistakes that we made here," he said.
Facebook first acknowledged last month that personal information about millions of users wrongly ended up in the hands of Cambridge Analytica.
Zuckerberg will testify about the matter next Tuesday and Wednesday during two US congressional hearings.
London-based Cambridge Analytica, which has counted US President Donald Trump's 2016 campaign among its clients, disputed Facebook's estimate of affected users. It said in a tweet on Wednesday it received no more than 30 million records from a researcher it hired to collect data about people on Facebook.
Zuckerberg said Facebook should have done more to audit and oversee third-party app developers like the one Cambridge Analytica hired in 2014.
Going forward, he said, Facebook was taking steps to restrict which personal data is available to third-party app developers, and he said it might take two more years to fix Facebook's problems.
Most of the up to 87 million people whose data was shared with Cambridge Analytica were in the US, Facebook Chief Technology Officer Mike Schroepfer wrote in a blog post.
Zuckerberg said Facebook came to the higher estimate by looking at the number of people who had downloaded a personality quiz app created by Cambridge University academic Aleksandr Kogan, or about 270,000 people, and then adding in the number of friends they had.
Cambridge Analytica has said that it engaged Kogan "in good faith" to collect Facebook data in a manner similar to how other third-party app developers have harvested personal information.
