Facebook CEO Mark Zuckerberg, in his first comments since the user-privacy crisis now engulfing the company broke, has admitted Facebook has made mistakes and outlined what it plans to do to restore trust with users.

News broke last Friday that Cambridge Analytica, a UK-based political data- analytics firm hired by the 2016 Trump campaign, got its hands on data for 50 million Facebook users - without the users' knowledge or consent.

"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," Zuckerberg wrote in a blog post Wednesday.

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Here's what Zuckerberg said Facebook will do: First, it will investigate all apps that had access to "large amounts of information" before Facebook changed its platform to reduce data access in 2014.

Second, Facebook will restrict developers' data access "even further to prevent other kinds of abuse," according to Zuckerberg. For example, it will remove developers' access to user data if you haven't used their app in three months.

Third, it will display a tool at the top of the News Feed with apps users have used and an easy way to revoke those apps' permissions to your data.

Facebook says the researcher that supplied the data to Cambridge Analytica, going back to 2013, lied to Facebook and violated its policies. The company barred Cambridge Analytica and its parent company from using its platform, and also says it no longer allows third-party apps to captured data the way that was done in this case.

"This was a breach of trust between (researcher Aleksandr) Kogan, Cambridge Analytica and Facebook," Zuckerberg wrote. "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."

The scandal has drawn renewed scrutiny on Facebook's data-handling practices from lawmakers and regulators, led some users to call for a boycott (via the hashtag #DeleteFacebook) and prompted lawsuits from shareholders and users.

It ignited a two-day selloff of Facebook stock, before shares recovered some ground Wednesday.