New Delhi: In the first ever official confirmation of the possible scope of the data leak, which was previously estimated in news reports, Facebook Inc said on Wednesday that personal information of as many as 87 million people, most of them in the US, may have been improperly shared with data firm Cambridge Analytica.

About 270,000 people downloaded a personality quiz app and shared information about themselves and their friends with a researcher, who then passed along the information to Cambridge Analytica, in a move that Facebook says was against its rules.

The 87 million figure is much higher than the 50 million people estimated in earlier reports. Facebook made the new disclosure in an online posting on Wednesday. Facebook said it will tell people, in a notice at the top of their news feeds starting April 9, if their information may have been improperly shared with Cambridge Analytica.

The revelation hints at the drilling chief executive officer Mark Zuckerberg will likely have to face when he testifies on the matter before Congress next week: How many other Cambridge Analytica-scale leaks of data are out there?

The company has been embroiled in controversy for weeks over the revelation that data was shared and then not deleted. It raised questions over the reams of data Facebook compiles on users, makes available to third parties, and what happens to it afterward.

Facebook made the announcement along with an update of its privacy policy. The new policy aims to explain the data it gathers on users more clearly, but doesn't actually change what it collects and shares.