Mark Zuckerberg has apologised over the Cambridge Analytica data scandal during a second day of questioning in a two congressional hearing.
The Facebook CEO admitted before 44 US Senators he failed to prevent data-mining firm from gathering personal information to influence elections.
“We didn’t take a broad enough view of our responsibility, and that was a big mistake,” Mr Zuckerberg said.
“It was my mistake and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here.”
He was questioned on a range of issues surrounding his social media platform including consumer privacy and Facebook’s handling of alleged Russian attempts at election interference.
He said the company is facing an “arms race” with Russia and was trying to change as a result of criticism towards the company.
“We’ve deployed new AI tools that do a better job of identifying fake accounts that may be trying to interfere in elections or spread misinformation,” Mr Zuckerberg said.
“There are people in Russia whose job it is to try and exploit our systems and other internet systems.”
“So this is an arms race.”
He said the company had to improve, with improvements to security expected, with the Russian interference “one of my greatest regrets.”
“They’re going to keep on getting better at this and we need to invest in keeping on getting better at this too,” he said.
“We’re going to have more than 20,000 people by the end of this year working on security and content review across the company.”
“We are going through a broad philosophical shift at the company.”
Facebook is facing falling confidence among users, advertisers, employees and investors, after admitting personal information of people mostly in the United States that used Facebook was used by Cambridge Analytica, a political consulting firm.
The company has also struggled with fake news and alleged foreign interference in elections.
It revealed in September that Russians used the social media platform under fake names in an attempt to influence US voters during months before and after the 2016 election.
US Special Counsel Robert Mueller charged 13 Russians and three Russian companies in February, with interference in the election through social media.
However, Mr Zuckerberg believed he was the right person to continue leading the social network he created.
Facebook shares closed with their biggest daily increase in two years.
They finished up 4.5 per cent to their highest level in almost three weeks.