Facebook chief technology officer, Mike Schroepfer, has revealed that 311,127 Australian Facebook users may have had their information "improperly shared" with Cambridge Analytica.
In March, Australia Information Commissioner, Timothy Pilgrim, said his office was making enquiries with Facebook to ascertain whether any personal information of Australians was involved.
Facebook said on Wednesday that the personal information of up to 87 million users, mostly (70.6 million) in the United States, 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 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 that 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.
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 week before the US House Energy and Commerce Committee.
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 that it received no more than 30 million records from a researcher it hired to collect data about people on Facebook.
Zuckerberg, on the call with reporters, said Facebook should have done more to audit and oversee third-party app developers like the one that Cambridge Analytica hired in 2014.
"Knowing what I know today, clearly we should have done more," he said.
Citizens from the Philippines (1.1 million), Indonesia (1.1 million), the United Kingdom (1 million), Mexico (789,000), Canada (622,000), India (562,000), Brazil (443,000) and Vietnam (427,000) are on the list of those who may have had their information accessed.
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.
The previous estimate of more than 50 million Facebook users affected by the data leak came from two newspapers, the New York Times and London's Observer, based on their investigations of Cambridge Analytica.
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.
The scandal has kicked off investigations by Britain's Information Commissioner's Office, the US Federal Trade Commission and by some 37 US state attorneys general.
Nigeria's government will investigate allegations of improper involvement by Cambridge Analytica in that country's 2007 and 2015 elections, a presidency spokesman said on Monday.
(Reporting by David Ingram in San Francisco; Additional reporting by Arjun Panchadar in Bengaluru and Eric Auchard in London; Editing by Lisa Shumaker; With ARN Staff)