Facebook founder Mark Zuckerberg has admitted his company "made mistakes" over the alleged misuse of users' data.
The social media giant's chief executive posted a long statement on his Facebook page explaining the steps he has taken, and will continue to take, to protect users.
Facebook saw $37bn (£26bn) wiped off its value amid concerns over the alleged harvesting of user data by UK political consultancy firm Cambridge Analytica.
Mr Zuckerberg had been criticised for his lack of response to the scandal, but he broke his silence on Wednesday evening.
"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," he said.
He said the company has a responsibility to protect data, "and if we can't then we don't deserve to serve you".
He went on to say the "most important actions to prevent this from happening again today we have already taken years ago".
"But we also made mistakes," he said, "there's more to do, and we need to step up and do it."
Cambridge Analytica, which was hired by Donald Trump's campaign team, has been accused of illegally harvesting the personal data of 50 million Facebook users.
Facebook is currently facing investigations by authorities in the UK, EU and the US and Mr Zuckerberg has been sent a formal request to appear before MPs and answer questions on the matter.
Facebook is currently trying to understand "exactly what happened" in order to prevent further breaches of this nature, the company's founder said.
The statement outlined a timeline of events leading to the situation as it stands today.
"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," Mr Zuckerberg says.
In 2014 Facebook made changes that meant the data that could be accessed by such apps would be dramatically limited.
It meant the apps "could no longer ask for data about a person's friends unless their friends had also authorised the app".
In 2015, Facebook learned from journalists at The Guardian that Mr Kogan had shared data from his app with Cambridge Analytica, which Facebook says "is against our policies" so they "immediately" banned Mr Kogan's app from its platform.
Mr Zuckerberg says Facebook demanded Mr Kogan and Cambridge Analytica delete all improperly acquired data, but says he learnt last week they had not deleted the data as they had previously certified, which led Facebook to "immediately banned them from using any of our services".
Cambridge Analytica says it deleted the data when it was asked to.
His statement set out a three-step plan to protect Facebook's users.
It will begin by investigating all apps that had access to large amounts of information before it changed its platform in 2014.
"If we find developers that misused personally identifiable information, we will ban them and tell everyone affected by those apps," he said.
It will also restrict data access, for example, if a user has not used an app in the last three months, the developers' access to the data will be removed.
Changes will also be made to allow users to understand more easily which apps are accessing their data.
Facebook will do this by displaying a new tool at the top of the News Feed which will allow users to easily see and revoke an app's access if they wish.
This tool already exists in privacy settings but putting it at the top of the News Feed will "make sure everyone sees it".
A poll by Sky Data has revealed 61% of Facebook users don't understand what data the social network can access.
As well as this, 80% said they didn't understand what Facebook did with the data it obtains and 65% said they trust Facebook less now than they did a week ago.
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Sky Data interviewed a nationally representative sample of 1,035 Sky customers by SMS on 21st March 2018. Data are weighted to the profile of the population.
For full Sky Data tables, please click here.