Facebook believes the data of up to 87 million people was improperly shared with the political consultancy Cambridge Analytica – many more than previously disclosed.
The BBC has been told that about 1.1 million of them are UK-based.
The overall figure had been previously quoted as being 50 million by the whistleblower Christopher Wylie.
Facebook chief Mark Zuckerberg said “clearly we should have done more, and we will going forward”.
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During a press conference he said that he had previously assumed that if Facebook gave people tools, it was largely their responsibility to decide how to use them.
The latest revelations came several hours after the US House Commerce Committee announced that Facebook’s founder, Mark Zuckerberg, would testify before it on 11 April.
Facebook’s share price has dropped sharply in the weeks since the allegations emerged.
In his Wednesday blog post, Mr Schroepfer detailed new steps being taken by Facebook in the wake of the scandal.
- a decision to stop third-party apps seeing who is on the guest lists of Events pages and the contents of messages posted on them
- a commitment to only hold call and text history logs collected by the Android versions of Messenger and Facebook Lite for a year. In addition, Facebook said the logs would no longer include the time of the calls
- a link will appear at the top of users’ News Feeds next week, prompting them to review the third-party apps they use on Facebook and what information is shared as a consequence
Facebook has also published proposed new versions of its terms of service and data use policy.
The documents are longer than the existing editions in order to make the language clearer and more descriptive.
Tinder users affected
Another change the company announced involved limiting the type of information that can be accessed by third-party applications.
Immediately after the changes were announced, however, users of the widely popular dating app Tinder were hit by login errors, leaving them unable to use the service.
A technical issue is preventing users from logging into Tinder. We apologize for the inconvenience and are working to have everyone swiping again soon.
— Tinder (@Tinder) April 4, 2018
End of Twitter post by @Tinder
Tinder relies on Facebook to manage its logins. Users reported that they had been signed out of the app and were unable to log in again.
Instead, the app repeatedly asks for more permissions to access a user’s Facebook profile information. Many were quick to link the outage to the changes announced by Facebook.
Y'all I just checked on my account and this is real. Facebook just broke Tinder. This is about to be America's loneliest Wednesday night in several years https://t.co/5KHe763wGY
— Casey Newton (@CaseyNewton) April 4, 2018
End of Twitter post by @CaseyNewton
The Cambridge Analytica scandal follows earlier controversies about “fake news” and evidence that Russia tried to influence US voters via Facebook.
Mr Zuckerberg has declined to answer questions from British MPs.
When asked about this by the BBC, he said he had decided that his chief technology officer and chief product officer should answer questions from countries other than the US.
He added, however, that he had made a mistake in 2016 by dismissing the notion that fake news had influenced the US Presidential election.
“People will analyse the actual impact of this for a long time to come,” he added.
“But what I think is clear at this point is that it was too flippant and I should never have referred to it as crazy.”