Zuck spoke and the world listened. 

But he may not have said enough to appease critics of the world's largest social network.

After five days of silence and with the hashtags #WheresZuck and #DeleteFacebook trending on Twitter, Facebook CEO Mark Zuckerberg on Wednesday addressed a major controversy over how London-based consultancy Cambridge Analytica misused personal data from 50 million Facebook users. In a 936-word post on his Facebook page, Zuckerberg acknowledged that Facebook had made "mistakes" that led to a "breach of trust between Facebook and the people who share their data with us and expect us to protect it."

In interviews with a few media outlets, including CNN, the New York Times and Wired later in the day, Zuckerberg talked about things it seemed Facebook would never talk about. Asked about government regulation, Zuckerberg said he'd be open to it, particularly regulation related to ad transparency. "I'm not sure we shouldn't be regulated," he said. He also said he'd consider testifying before Congress -- if he was the person at Facebook with the most information about the topic in question. Prominent senators, including Democrats Amy Klobuchar and Mark Warner, have called for him to testify. (Facebook already testified before Congress last November over its role in the presidential election, but the company sent its top lawyer, and not Zuckerberg.)

The interviews seemed intended to cast Zuckerberg as a chastened chief executive, opening up because Facebook's reputation had taken a beating for days as the public, privacy groups, legislators and Facebook users demanded answers. The company also took a financial hit, with its stock dropping 8.5 percent since news broke about the data exploit on March 16. 

Both Zuckerberg and Sheryl Sandberg, Facebook's COO and the other public face of the company, have said they're "sorry" about the incident. But Sandberg's apology went a little further, admitting, "I am so sorry that we let so many people down."

"This is absolutely a turning point," said Bob O'Donnell, an analyst with the research firm Technalysis. "It's angered a lot of people."

Facebook was criticized last week for having its platform exploited by Cambridge Analytica, a digital analytics firm hired by the Trump presidential campaign. According to Facebook, personal data from about 300,000 users was originally collected by a Cambridge lecturer named Aleksandr Kogan in 2013 for a personality quiz app. But given the way Facebook worked at the time, Kogan was able to access data from "tens of millions" of friends of those users, Zuckerberg said. While Kogan collected the data legitimately, he then violated Facebook's terms by passing the information to Cambridge Analytica.

The social network, which boasts about 2 billion monthly users, found out about the infraction in 2015 but didn't inform the public. Instead, Facebook demanded that all the parties involved destroy the information. But reports late last week revealed that not all the data had in fact been deleted. Whistleblower Chris Wylie, a former data scientist for Cambridge Analytica, brought that story to the New York Times and The Guardian. The blowup then raised questions about Facebook's treatment of data and whether it's doing enough to protect it.

The situation was exacerbated by the lack of response from Facebook leadership. Sandberg said she regrets not speaking up sooner. "Sometimes, and I would say certainly this past week, we speak too slowly," she said on CNBC. "If I could live this past week again, I would have definitely had Mark and myself out speaking earlier, but we were trying to get to the bottom of this."

'Lingering under the surface'

Part of the reason the public outcry has been so loud is that people have become increasingly fed up with the social media giant, O'Donnell said. Zuckerberg and his team were already under fire for Facebook's mishandling of fake news spread on its platform and for meddling by Russian trolls during the 2016 presidential election. "It's been lingering under the surface for a while," O'Donnell said. 

Zuckerberg and Facebook COO Sheryl Sandberg on Wednesday vowed to make changes to the platform so a similar exploit would never happen again. Facebook said it will "investigate" all apps that have access to large amounts of data, and restrict developers' data access even further. Zuckerberg told the New York Times on Wednesday that the number of apps is in "the thousands."

He also said that Facebook will notify "anyone whose data may have been shared."

For Facebook users, if you haven't used an app in three months, the company will automatically remove its access to your data. When you sign into apps, you'll also give developers less of your personal information -- only your name, email and Facebook profile photo. The company will also start presenting you with a tool at the top of your news feeds that shows what apps you've been using so you can more easily manage your data settings. 

In addition, the social media giant plans to audit any app it suspects of suspicious behavior. If developers don't agree to the audit, they'll be banned from the platform. Developers will also have to sign a contract in order to ask people for access to their data. 

"Facebook's proposals are a good start, but they don't go far enough," Corynne McSherry, legal director of the Electronic Frontier Foundation, a digital rights group, said in a statement. "They've already shown us that we can't trust them. We need real transparency and accountability."

Klobuchar, the Minnesota senator, also called the changes a "start" but said Zuckerberg still needs to testify before Congress. "Facebook should show good faith & support the Honest Ads Act," she tweeted on Wednesday. "To truly regain the public's trust, Facebook must make significant changes so this doesn't happen again."

"Mea culpas are no substitute for questions and answers under oath," Sen. Richard Blumenthal, a Democrat from Connecticut and a member of the Judiciary Committee, told Bloomberg News. "Congress has failed to hold Facebook accountable and legislate protections on privacy, which are manifestly necessary."

Still, this may be a new day for Zuckerberg -- at least in terms of his accessibility to those seeking answers about how the social network behaves. "There's an element of accountability where I should be out there doing more interviews," he told CNN. 

"Over the course of Facebook, I've made all kinds of different mistakes, whether that's technical mistakes or business mistakes or hiring mistakes. We've launched product after product that didn't work," Zuckerberg said in his interview with the New York Times.

"I don't know that it's possible to know every issue that you're going to face down the road," he continued. "But we have a real responsibility to take all these issues seriously as they come up, and work with experts and people around the world to make sure we solve them."

First published March 22, 5:10 a.m. PT
Update, 2:13 p.m.: Adds comments from Facebook COO Sheryl Sandberg.

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