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The social media giant is expected today to begin notifying up to 87 million users whose personal information was accessed by a political consultancy that worked for Donald Trump's presidential campaign.
Facebook plans to place a link at the top of each user's news feed informing them if their data was "improperly shared" in the so-called Cambridge Analytica scandal.
The move comes a day before Mark Zuckerberg, the California-based company's founder and chief executive officer, is scheduled to testify before Congress.
Zuckerberg was on Capitol Hill on Monday in meetings with members of Congress prior to his testifying. He wore a suit rather than his trademark outfit of a T-shirt and jeans.
Cambridge Analytica, a data-mining firm, allegedly improperly accessed personal data on Facebook through a third-party quiz app, and a whistleblower says the company used the information to build psychological profiles in an effort to target voters with political ads.
Facebook Chief Technology Officer Mike Schroepfer announced last week that the Cambridge Analytica breach affected as many as 87 million users, a number that has grown several times since the scandal became public last month. Facebook says the bulk of affected users are in the United States.
The scandal comes about seven years after Facebook signed a consent decree with the U.S. Federal Trade Commission promising it would not share people's personal data without permission from the users.
Cambridge Analytica has denied wrongdoing and in a statement last week said it had data from only 30 million users.
Whether a user's data was accessed or not, Facebook plans to show all people on the site the third-party apps authorized to use their information and provide instructions on how to delete, the company said.