Facebook chief Mark Zuckerberg placed the blame for privacy and security lapses at the world's largest social network squarely on himself as he girded Monday for appearances this week on Capitol Hill before angry lawmakers.
In prepared remarks released by a congressional panel, Zuckerberg admitted he was too idealistic and failed to grasp how the platform - used by two billion people - could be abused and manipulated.
The 33-year-old is to testify before senators on Tuesday and House lawmakers on Wednesday amid a firestorm over the hijacking of data on millions of Facebook users by the British firm Cambridge Analytica, which worked with Donald Trump's campaign.
Zuckerberg ditched his trademark T-shirt for a suit and tie as he made the rounds on Capitol Hill for private meetings with lawmakers ahead of the hearings - a key test for the Facebook founder.
Republican Senator John Kennedy, in a preview of the grilling planned for the Facebook chief, said Zuckerberg needed to do more than just apologize and accept responsibility.
"I hope he uses his time to say, 'Hey, I'm on this. Here's how we're going to solve the privacy issue, and here's how we're going to solve the problem of poison being spread on social media platforms,'" the Louisiana senator said.
"My biggest worry is that Facebook can't do that."
In his written testimony released by the House Energy and Commerce Committee, Zuckerberg said: "We didn't take a broad enough view of our responsibility, and that was a big mistake. It was my mistake, and I'm sorry.
"I started Facebook, I run it and I'm responsible for what happens here," he added.
Zuckerberg called Facebook "an idealistic and optimistic company" that "focused on all the good that connecting people can bring."
But he acknowledged that "it's clear now that we didn't do enough to prevent these tools from being used for harm as well."
The Facebook chief said he has called for more security investments, stressing that "protecting our community is more important than maximizing our profit."
Investigating every app
Zuckerberg recounted a list of steps announced by Facebook aimed at averting a repeat of the improper use of data by third parties like Cambridge Analytica, and noted that other applications were also being investigated to determine if they did anything wrong.
"We're in the process of investigating every app that had access to a large amount of information before we locked down our platform in 2014," said Zuckerberg.
"If we detect suspicious activity, we'll do a full forensic audit. And if we find that someone is improperly using data, we'll ban them and tell everyone affected."
After meeting with Zuckerberg on Monday, Senator Bill Nelson told reporters that he appears to be taking the matter seriously.
"I believe he understands that regulation could be right around the corner," Nelson said.
Nelson said lawmakers would be looking at other social media sites in determining any new regulations.
Facebook "happens to be the point of the spear, but all these other app sites that get your personal data, that's another way of us losing our privacy," the Florida senator added.
Facebook has taken a series of proactive steps to make up for massive lapses in protecting user data, as lawmakers signaled they intend to get tough on privacy.
Last week, the company announced new privacy tools for user newsfeeds, and said it would notify the 87 million users affected by the data hijacking scandal, amid probes underway on both sides of the Atlantic.
Over the weekend, Facebook said it had suspended another data analysis firm, US-based Cubeyou, after reports that it had used private data harvested from psychological testing apps for commercial purposes.
It also suspended the Canadian firm AggregateIQ over apparent collaboration with Cambridge Analytica.
Backing 'Honest Ads'
On Friday, Facebook sought to quell some concerns over political manipulation of its platform by announcing support for the "Honest Ads Act" that requires election ad buyers to be identified, and to go further with verification of sponsors of ads on key public policy issues.
Zuckerberg said the change means Facebook will hire "thousands" to get the new system in place ahead of US midterm elections in November.
"We're starting this in the US and expanding to the rest of the world in the coming months," he said.
Facebook agreed to supply proprietary data for a study on its role in elections and democracy worldwide.
It has said it has seen little impact on its business from the privacy scandal despite a #deleteFacebook movement and concerns from advertisers.
But Brian Wieser of Pivotal Research said the entire digital advertising industry, of which Google and Facebook are the leaders, could be impacted by the scandal.
He said the changes announced by Facebook and Google restricting third-party access "indicate a higher likelihood that both companies will 'raise their walls.'"