The personal information of up to 87 million users may have been "improperly shared" with political consulting firm Cambridge Analytica, Facebook said on Wednesday.
The social media giant's Chief Technology Officer, Mike Schroepfer, revealed the number in a blog post, and said the tens of millions affected were "mostly in the US."
It was previously believed that around 50 million users were impacted by the data breach.
However, Cambridge Analytica stated that it "licensed data from [Global Science Research] for 30 million individuals, not 87 million," and added the data mining firm "did not use GSR Facebook data or any derivatives of this data in the US presidential election."
Global Science Research is the company co-founded by Aleksandr Kogan that harvested Facebook's data using a personality app and later shared the data with Cambridge Analytica.
Facebook's blog post also detailed the company's efforts to be more transparent about changes regarding security on the social media platform and its user data.
CEO Mark Zuckerberg, who will testify next week on Capitol Hill following the scandal, told reporters on Wednesday he made a "huge mistake" in failing to take a broad enough view of what Facebook's responsibility in the world is.