Eighty-seven million Facebook users around the world will find out on Monday if their details were shared with Cambridge Analytica in one of the social network’s largest data breaches.
The firm said affected users would receive a detailed message on their news feeds. The majority of those whose information was shared with the data analytics firm – about 70 million – are in the US.
More than 1 million people in each of the UK, Philippines and Indonesia may also have had their personal information harvested as well as 310,000 Australian Facebook users.
All 2.2 billion Facebook users will receive a notice titled “Protecting Your Information” with a link to see what apps they use and what information has been shared with those apps. They will be able to shut off apps individually or turn off third-party access.
It comes after the Observer revealed that Cambridge Analytica, which worked with Donald Trump’s election team, acquired millions of profiles of US citizens and used the data to build a software program to predict and influence voters.
Facebook discovered the information had been harvested in late 2015 but failed to alert users at the time.
The information was collected through an app called thisisyourdigitallife, built by the Cambridge University academic Aleksandr Kogan in collaboration with Cambridge Analytica.
Hundreds of thousands of users were paid a fee to take a personality test and consented to have their data collected. The app also harvested information about the participants’ friends.
Facebook’s CEO, Mark Zuckerberg, who is expected to testify before Congress this week, acknowledged that he made a “huge mistake” in failing to take a broad enough view of the company’s responsibilities.
Cambridge Analytica whistleblower Christopher Wylie previously estimated that more than 50 million people were compromised by the personality test.
In an interview aired on Sunday on NBC’s Meet the Press, Wylie said the true number could be even higher than 87 million. He said: “I know that Facebook is now starting to take steps to rectify that and start to find out who had access to it and where it could have gone, but ultimately it’s not watertight to say that, you know, we can ensure that all the data is gone forever.”
Last month, he told the Observer: “We exploited Facebook to harvest millions of people’s profiles. And built models to exploit what we knew about them and target their inner demons. That was the basis the entire company was built on.”
Zuckerberg said Facebook came up with the 87 million figure by calculating the maximum number of friends that users could have had while Kogan’s app was compiling data.
Cambridge Analytica insisted last week that it had information for only 30 million Facebook users.
