Facebook has said it now believes up to 87 million people's data was improperly shared with the political consultancy Cambridge Analytica.
The figure previously quoted by the whistleblower Christopher Wylie had been 50 million.
In addition, the social network confirmed it thought some of the data was about people based outside the US.
The details were revealed in a blog by the tech firm's chief technology officer, Mike Schroepfer.
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