Facebook now says the data of up to 87 million people was improperly shared with political consultancy firm, Cambridge Analytica.
The figure which is 37 million more than previously reported was buried at the end of a blogpost by Facebook's technology officer, Mike Schroepfer.
The news comes a week before CEO Mark Zuckerberg is due to face questioning from members of the US Congress over the data scandal.
The British-based consultancy firm that worked with Donald Trump’s election team and the Brexit campaign is said to have used the data it acquired to build a software programme to predict and influence voters.
Facebook discovered the information had been harvested by a third party in late 2015 but failed to alert users at the time.