Facebook boss Mark Zuckerberg took out full page adverts in six British Sunday newspapers to apologise for the “breach of trust” which saw the data of millions of people leaked without their knowledge.

The apology, also published in three US newspapers, came after Facebook’s stock market value plunged by $58bn last week in the wake of reporting led by The Observer’s Carole Cadwalladr.

It is alleged that London-based data firm Cambridge Analytica created a personality quiz to harvest the personal data of 50m Facebook users in 2014.

Facebook claims to have ordered Cambridge Analytica to delete the data in 2015, but it was informed by The Observer, the New York Times and Channel 4 last week that the firm had not done so.

In the UK, the advert, in the form of a letter written by Zuckerberg, was printed in the Observer, The Sunday Times, Sunday Telegraph, Mail on Sunday, Sunday Express and Sunday Mirror.

Fair to say Facebook paid a fortune for this. Here is Mark Zuckerberg's full-page personal apology on the back pages of the Mail on Sunday, Sunday Times, Sunday Telegraph, Sunday Mirror and Observer: pic.twitter.com/80WBYNXysn

— Dan Bloom (@danbloom1) March 25, 2018

In the US, the same advert was placed in the New York Times, which collaborated with The Observer and Channel 4 on the investigation, the Washington Post and the Wall Street Journal.

The advert, which ended with Zuckerberg’s signature, said: “We have a responsibility to protect your information. If we can’t, we don’t deserve it.

“You may have heard about a quiz app built by a university researcher that leaked Facebook data of millions of people in 2014.

“This was a breach of trust, and I’m sorry we didn’t do more at the time. We’re now taking steps to make sure this doesn’t happen again.”

Cadwalladr, who broke the story in The Observer last weekend, criticised Zuckerberg (pictured) for advertising in the newspapers but declining interview requests.

She tweeted: “Dear Zuck, we printed your words because you paid us. But have this for free: advertising is not accountability. Why did you refuse our interview request?”

Facebook threatened to take legal action against The Observer on 16 March, a day before the story broke online. Facebook’s head of news partnerships Campbell Brown has since said it was not the company’s “wisest move”.

Speaking at the Financial Times’ Future of News Conference in New York on Thursday, he said: “It was a mistake to not have addressed [the data leak] then, and if it were me I would not have threatened to sue The Guardian. Probably not our wisest move.”

The advert also explained what action Facebook is taking in the wake of the scandal, which saw data harvested through a personality quiz app and allegedly used to target voters during the Brexit and US presidential election campaigns.

Zuckerburg said: “We’ve already stopped apps like this from getting so much information. Now we’re limiting the data apps get when you sign in using Facebook.

“We’re also investigating every single app that had access to large amounts of data before we fixed this. We expect there are others. And when we find them, we will ban them and tell everyone affected.

“Finally, we’ll remind you which apps you’ve given access to your information – so you can shut off the ones you don’t want anymore.

“Thank you for believing in this community. I promise to do better for you.”

Picture: Reuters/Stephen Lam