Facebook Chief Executive Mark Zuckerberg apologised to Britons on Sunday in full-page ads in almost all British newspapers for a huge data privacy scandal.
"We have a responsibility to protect your information. If we can't we don't deserve it," the ad read.
Zuckerberg explained there was a quiz developed by a university researcher "that leaked Facebook data of millions of people in 2014".
"This was a breach of trust, and I'm sorry we didn't do more at the time. We're now taking steps to make sure this doesn't happen again," he said.
The statement reflects public statements Zuckerberg made last week after the row prompted investigations in Europe and the United States, and sent Facebook's share price plunging.
Zuckerberg assured that of no such data breach in future as Facebook had changed the rules.
"We're also investigating every single app that had access to large amounts of data before we fixed this. We expect there are others," he wrote.
"And when we find them, we will ban them and tell everyone affected."
There was no mention of the British firm accused of using the data, Cambridge Analytica, which worked on US President Donald Trump's 2016 campaign.
It too has blamed the University of Cambridge researcher, Alexsandr Kogan, for any potential breach of data rules.
Kogan created a lifestyle quiz app for Facebook which was downloaded by 270,000 people, but allowed access to tens of millions of their contacts.
Facebook says he passed this to Cambridge Analytica without its knowledge. Kogan says he is being made a scapegoat.
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