Mark Zuckerberg has admitted his company failed to take a broad enough view of its responsibility which lead to the information of up to 87 million members being improperly shared with a political consultancy firm.
The figure is 37 million more than previously reported by Facebook which was buried at the end of a blogpost by the company's technology officer, Mike Schroepfer.
"It's clear now that we didn't do enough," Mark Zuckerberg said. "We didn't focus enough on preventing abuse and thinking through how people could use these tools to do harm as well.
"And that goes for fake news, foreign interference in elections, hate speech, in addition to developers and data privacy.
"We didn't take a broad enough view of what our responsibility is, and that was a huge mistake. It was my mistake."
Zuckerberg to face US Congress over scandal
Mr Zuckerberg is due to front two United States congressional hearings about the scandal which involved British-based consultancy firm, Cambridge Analytica, next week.
The firm worked with Donald Trump's election team and the Brexit campaign, and is said to have used the information to build a software programme to predict and influence voters.
Cambridge Analytica tweeted that it "...licensed data from 30 million individuals, not 87 million. We did not receive more than 30 million records from research company GSR".
Associated Press Technology Editor, David Hamilton, said the Facebook CEO would "face a lot of questions about these various privacy scandals" at the hearings.
"How did they happen? Why wasn't Facebook minding the store? Are their current measures sufficient or are they tinkering around the edges? And can people feel secure about their data on Facebook?" he said.
The scandal wiped more than 65 billion Euros from the company's market value last month.
Mr Zuckerberg said it had not affected the site's usage or advertising sales, despite the #DeleteFacebook which trended on Twitter.