Facebook CEO Mark Zuckerberg says his company "made mistakes" in relation to Cambridge Analytica.
He's broken his silence over the apparent data breach, which is being investigated by authorities in Ireland, the EU, UK and US.
UK-based data firm Cambridge Analytica, which was hired by Donald Trump's campaign team, is accused of using millions of Facebook profiles without authorisation to predict and influence the US election.
The board of Cambridge Analytica announced yesterday it had suspended its CEO Alexander Nix pending a full independent investigation.
In a statement posted on Facebook tonight, Mr Zuckerberg says: "We have a responsibility to protect your data, and if we can't then we don't deserve to serve you."
Posting a timeline of events, he says that in 2013, a Cambridge University researcher named Aleksandr Kogan created a personality quiz app, which was installed "by around 300,000 people who shared their data as well as some of their friends' data."
Mr Zuckerberg explains: "In 2014, to prevent abusive apps, we announced that we were changing the entire platform to dramatically limit the data apps could access.
"Most importantly, apps like Kogan's could no longer ask for data about a person's friends unless their friends had also authorized the app."
Then he says: "In 2015, we learned from journalists at The Guardian that Kogan had shared data from his app with Cambridge Analytica.
"It is against our policies for developers to share data without people's consent, so we immediately banned Kogan's app from our platform, and demanded that Kogan and Cambridge Analytica formally certify that they had deleted all improperly acquired data. They provided these certifications."
Facebook founder Mark Zuckerberg is pictured during a joint press conference on the sidelines of the G8 summit in Deauville, France in 2011 | Image: Orban Thierry/ABACA/PA Images
He says the company then learned "from The Guardian, The New York Times and Channel 4" that Cambridge Analytica may not have deleted the data as they had certified.
"We immediately banned them from using any of our services. Cambridge Analytica claims they have already deleted the data and has agreed to a forensic audit by a firm we hired to confirm this. We're also working with regulators as they investigate what happened."
"This was a breach of trust between Kogan, Cambridge Analytica and Facebook. But it was also a breach of trust between Facebook and the people who share their data with us and expect us to protect it. We need to fix that."