Mark Zuckerberg is finally breaking his silence five days after a data scandal engulfed Facebook.

The Facebook (FB) CEO pledged Wednesday to take a series of steps to protect data and fix what he called a "breach of trust" between the social network and its users.

"We have a responsibility to protect your data, and if we can't then we don't deserve to serve you," Zuckerberg wrote in a Facebook post. "I've been working to understand exactly what happened and how to make sure this doesn't happen again."

Zuckerberg spoke with CNN's Laurie Segall in an interview broadcast on "Anderson Cooper 360" Wednesday night.

News broke this weekend that Cambridge Analytica, a data firm with ties to President Donald Trump's campaign, reportedly accessed information from about 50 million Facebook users without their knowledge.

Facebook says the data was initially collected by a professor for academic purposes in line with its rules. The information was later transferred to third parties, including Cambridge Analytica, in violation of Facebook's policies.

Related: Tune in to CNN tonight at 9 p.m. ET for Zuckerberg interview

The controversy wiped away nearly $50 billion from Facebook's stock price earlier this week and prompted politicians on both sides of the Atlantic to call for Zuckerberg to testify.

Facebook is now facing lawsuits from investors and users as well as a "delete Facebook" movement. The latest member of the latter: Brian Acton, the cofounder of WhatsApp, which Facebook acquired for $19 billion in 2014.

In his post Wednesday, Zuckerberg said Facebook will take steps to further restrict developers' access to user data, including automatically removing access for any app the user hasn't opened in at least three months.

Facebook will also promote an existing tool that helps users revoke permissions of apps accessing their data. The tool will appear at the top of the News Feed page in the next month.

Zuckerberg said Facebook is "working with regulators" conducting investigations into the Cambridge Analytica issue.

Related: What you need to know about Facebook's data debacle

"I started Facebook, and at the end of the day I'm responsible for what happens on our platform," Zuckerberg said. "We will learn from this experience to secure our platform further and make our community safer for everyone going forward."

Sheryl Sandberg, Facebook's COO, also spoke out for the first time since the scandal erupted, calling it "a major violation of peoples' trust."

-- CNN's Charles Riley and Jackie Wattles contributed to this report.