Facebook to alert users affected by Cambridge Analytica data breach

Facebook is to begin alerting users whose private data may have been compromised in the Cambridge Analytica scandal.

Starting on Monday, the 87 million users who might have had their data shared with Cambridge Analytica will get a detailed message on their news feeds.

Facebook said most of the affected users (more than 70 million) are in the US, though there are more than a million each in the Philippines, Indonesia and the UK.

Chief executive Mark Zuckerberg acknowledged that he made a “huge mistake” in failing to take a broad enough view of what Facebook’s responsibility is in the world. He is set to testify before Congress next week.

Cambridge Analytica whistleblower Christopher Wylie previously estimated that more than 50 million people were compromised by a personality quiz that collected data from users and their friends. In an interview aired on Sunday on NBC’s Meet The Press, Mr Wylie said the true number could be even larger than 87 million.

The app vacuumed up not just the data of the people who took it, but also — thanks to Facebook’s loose restrictions — data from their friends, too, including details that they had not intended to share publicly.

Facebook later limited the data apps can access, but it was too late in this case.

Mr Zuckerberg said Facebook came up with the 87 million figure by calculating the maximum number of friends that users could have had while Mr Kogan’s app was collecting data.

The company does not have logs going back that far, he said, so it cannot know exactly how many people may have been affected.

Cambridge Analytica said in a statement on Wednesday that it had data for only 30 million Facebook users.