Mark Zuckerberg finally addressed the Cambridge Analytica scandal on Wednesday afternoon after five days of deafening silence but did not apologize for the fact that 51 million Facebook users' information was taken without their knowledge.

In a lengthy post at 3.50pm, Zuckerberg offered his timeline of the events which led to the revelation this week that the shadowy data firm which shaped Trump's campaign and has been linked to Brexit improperly harvested tens of millions of users' data in 2013 by buying it from an app.

Facebook COO Sheryl Sandberg posted a coordinated post at the same time saying she 'deeply regrets' the scandal but did not apologize for it either.

Stopping short of apologizing outrightly, Zuckerberg said 'the good news' was that Facebook had changed its practices years ago to stop apps from accessing so much information.

He did acknowledge that the breach happened under his watch and said the company was now working on ways to win back users' trust.

'I started Facebook, and at the end of the day I'm responsible for what happens on our platform.

'I'm serious about doing what it takes to protect our community.

'While this specific issue involving Cambridge Analytica should no longer happen with new apps today, that doesn't change what happened in the past.

Scroll down for full statement

Mark Zuckerberg broke his silence over the Cambridge Analytica scandal on Wednesday in a lengthy Facebook post shared at 3.50pm

'We will learn from this experience to secure our platform further and make our community safer for everyone going forward,' he said.

His announcement sent Facebook's struggling stock back up to $169.39 before the final bell.

At 1.30pm, after news emerged that he was due to address the scandal, the stock surpassed the $170 mark for the first time since Monday. Before the scandal, it was $185.

In his statement on Wednesday, Zuckerberg said that while it was 'his responsibility' what happened at Facebook, the company was duped by Aleksandr Kogan, the researcher who sold the information to Cambridge Analytica, just as the people who gave him their details were.

He conceded that it was a 'breach of trust between Facebook and the people who share their data with us and expect us to protect it'.

Among the changes he plans to make now is a tool which will allow Facebook users to see which apps have their information from when they allowed them access to it before the 2014 change.

It will appear on users' news feeds within the next month.

Facebook said it also plans to go back and analyse those apps to examine what information they have.

If any do not comply with their requests to audit them, they will be banned, he said.

The announcement sent Facebook's struggling stock back up after a treacherous few days

MARK ZUCKERBERG'S STATEMENT ON CAMBRIDGE ANALYTICA I want to share an update on the Cambridge Analytica situation -- including the steps we've already taken and our next steps to address this important issue. We have a responsibility to protect your data, and if we can't then we don't deserve to serve you. I've been working to understand exactly what happened and how to make sure this doesn't happen again. The good news is that the most important actions to prevent this from happening again today we have already taken years ago. But we also made mistakes, there's more to do, and we need to step up and do it. Here's a timeline of the events: In 2007, we launched the Facebook Platform with the vision that more apps should be social. Your calendar should be able to show your friends' birthdays, your maps should show where your friends live, and your address book should show their pictures. To do this, we enabled people to log into apps and share who their friends were and some information about them. In 2013, a Cambridge University researcher named Aleksandr Kogan created a personality quiz app. It was installed by around 300,000 people who shared their data as well as some of their friends' data. Given the way our platform worked at the time this meant Kogan was able to access tens of millions of their friends' data. 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. We also required developers to get approval from us before they could request any sensitive data from people. These actions would prevent any app like Kogan's from being able to access so much data today. 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. Last week, we 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. In this case, we already took the most important steps a few years ago in 2014 to prevent bad actors from accessing people's information in this way. But there's more we need to do and I'll outline those steps here: First, we will investigate all apps that had access to large amounts of information before we changed our platform to dramatically reduce data access in 2014, and we will conduct a full audit of any app with suspicious activity. We will ban any developer from our platform that does not agree to a thorough audit. And if we find developers that misused personally identifiable information, we will ban them and tell everyone affected by those apps. That includes people whose data Kogan misused here as well. Second, we will restrict developers' data access even further to prevent other kinds of abuse. For example, we will remove developers' access to your data if you haven't used their app in 3 months. We will reduce the data you give an app when you sign in -- to only your name, profile photo, and email address. We'll require developers to not only get approval but also sign a contract in order to ask anyone for access to their posts or other private data. And we'll have more changes to share in the next few days. Third, we want to make sure you understand which apps you've allowed to access your data. In the next month, we will show everyone a tool at the top of your News Feed with the apps you've used and an easy way to revoke those apps' permissions to your data. We already have a tool to do this in your privacy settings, and now we will put this tool at the top of your News Feed to make sure everyone sees it. Beyond the steps we had already taken in 2014, I believe these are the next steps we must take to continue to secure our platform. I started Facebook, and at the end of the day I'm responsible for what happens on our platform. I'm serious about doing what it takes to protect our community. While this specific issue involving Cambridge Analytica should no longer happen with new apps today, that doesn't change what happened in the past. We will learn from this experience to secure our platform further and make our community safer for everyone going forward. I want to thank all of you who continue to believe in our mission and work to build this community together. I know it takes longer to fix all these issues than we'd like, but I promise you we'll work through this and build a better service over the long term. Advertisement

Sheryl Sandberg, Facebook's COO, also acknowledged the scandal but did not apologize either.

She shared Zuckerberg's post and said she 'deeply regrets' that users felt deceived by the social network.

'We know that this was a major violation of people's trust, and I deeply regret that we didn't do enough to deal with it.

'We have a responsibility to protect your data - and if we can't, then we don't deserve to serve you,' she said.

The sequence of events is as follows.

Sheryl Sandberg, Facebook's COO, said she 'deeply regrets' the breach of trust but did not apologize either

In 2013, Cambridge professor Aleksandr Kogan used his app, This Is Your Digital Life, to ask 270,000 Facebook users questions about their personalities.

By answering them, the users granted Kogan access to not only their profiles but to those of their friends.

He subsequently sold that information to Cambridge Analytica for $51million.

Facebook changed its rules in 2014 to limit what data such apps could access.

A year later, it learned that Kogan had sold his findings and contacted both him and Cambridge Analytica to tell them to delete the data which they promised to do.

Last week, Facebook made its announcement that it had suspended Cambridge Analytica after being warned of looming media reports that claimed not all of the information had been destroyed.

Those reports, which were informed by the accounts of whistleblowers who worked at the firm, also revealed the true scale of the breach.

The revelations kicked off a chain reaction of events including investigations in both Washington DC and Westminster into Cambridge Analytica practices.

Christopher Wylie, (left) who describes himself as one of the company's co-founders turned whistleblowers, has revealed how Cambridge Analytica paid $1million for the data of 51 million Facebook users which had been harvested through a personality quiz called This Is Your Digital Life. It was founded by Aleksandr Kogan (right) who sold the information to Cambridge Analytica

It was Stephen Bannon (pictured) who approved spending almost $1million to acquire data – including from Facebook – in 2014, Wylie said

WHAT IS FACEBOOK DOING TO FIX IT 1. Investigate apps which used old system to get user information Apps can no longer access the same amount of information that Kogan did through quizzes thanks to a 2014 change in Facebook policy however it remains unclear how many took advantage of the old rules before they changed. On Wednesday, Zuckerberg said Facebook's first step was to go back and look at what they still know. 2. Make the rules even tighter for app developers If a person has not engaged with an app for three months, Facebook will remove their access to you. They will also restrict what information they do get in the first place to only your name, profile photo, and email address. If they want more, they will have to sign a contract and get approval 3. Introduce tool to show what companies already know about you The tool will appear in the next month or so on users' news feeds Advertisement

The scandal has sent Facebook's once unstoppable stock tumbling and sparked a mass boycott of the social network by suspicious users who fear their data is not safe.

Among those who denounced the site was the one of the founders of WhatsApp, who Zuckerberg made a billionaire when he bought the messaging app.

Alexander Nix, the CEO of Cambridge Analytica, has been suspended and key Facebook figures, namely its head of security, have left their roles.

Cambridge Analytica claims it did delete all of the information and that they did not know they were wrong to purchase it in the first place.

They have allowed Facebook to carry out an audit of its books and have shifted the blame onto Kogan.

He complains that he has been made the scapegoat.

Wylie, who used to work for the firm but who has come forward amid a crisis of conscience, said it was Steve Bannon, Trump's former campaign chief executive, who masterminded the company.

'We had to get Bannon to approve everything at this point.

'Bannon was Alexander Nix's boss. Alexander Nix didn't have the authority to spend that much money without approval,' Chris Wylie, who used to work for the firm, told The Washington Post.

Hypocrisy: Carol Davidsen, (left) who worked as the media director at Obama for America, claims Facebook allowed them to mine American users' profiles in 2012 because they were supportive of the Democrats

WhatsApp co-founder Brian Acton, who sold the app to Facebook for 19 billion dollars in 2014, was one of thousands who vowed to leave Facebook on Tuesday

Cambridge Analytica is funded largely by Robert and Rebekah Mercer, a powerhouse, father-daughter duo who are also behind Trump Super PACs and Breitbart News.

The row has sparked accusations of hypocrisy from right-leaning minds who say Facebook is only outraged that it was a conservative firm which gained the data and not one it supports.

This allegation was all but confirmed by a member of President Obama's 2012 campaign who claimed they were given similar access willingly because Zuckerberg and his executives were 'on our side'.

In the UK, Cambridge Analytica is facing separate allegations over its rumored involvement in Brexit.

According to one founder of a Leave campaign, Nix, the CEO, offered up millions of dollars in illegal foreign support from the US to further the campaign.

He denies that the firm was ever involved and testified as much in front of MPs.

Nix was suspended after being caught on tape boasting about the company's work with foreign governments.