Mark Zuckerberg's testimony made him billions richer

Mark Zuckerberg's net worth was boosted by US$3 billion during his first Congressional testimony on Tuesday.

He kept his cool as he answered five hours of questions from 44 US senators, who were trying to decide whether Congress should intervene with regulations on Facebook.

Mr Zuckerberg repeated apologies he previously made for a range of problems that have beset Facebook, from a lack of data protection to Russian agents using the social media site to influence US elections.

During the hearing, Facebook shares made a noticeable jump, gaining 4.5 percent, adding $20 billion to its market cap - the biggest daily gain in nearly two years. The rise added US$3 billion (NZD $4.8 billion) to Mr Zuckerberg's fortune.

Facebook shares are still down 6.5 percent on the same time last year, after taking massive hit when privacy concerns first arose last month.

The shares fell steeply after it came to light that millions of users' personal information was harvested from Facebook by Cambridge Analytica, a political consultancy that has counted US President Donald Trump's election campaign among its clients.

The latest estimate of affected users is up to 87 million.

That disclosure pitched Facebook into a crisis of confidence among users, advertisers, employees and investors who were already struggling with Facebook's reaction to fake news and its role in the 2016 election.

Mr Zuckerberg reportedly hired a team of experts to teach him how to behave in a personable manner throughout the first testimony. He also hired a team from the law firm WilmerHale to coach him through questions that may have been asked.

Wearing a dark suit and tie instead of his typical T-shirt and jeans, Mr Zuckerberg remained largely unruffled and serious as senators questioned him. But some senators did provoke a reaction.

He was asked whether Facebook was a monopoly. "It certainly doesn't feel that way to me," he said, breaking into a smile as the audience laughed.

Facebook disclosed in September that Russians under fake names used the social network to try to influence US voters in the months before and after the 2016 election, writing about inflammatory subjects, setting up events and buying ads.

When asked if there was overlap between Cambridge Analytica's harvested user data and the political propaganda pushed by the Kremlin-linked Internet Research Agency during the 2016 presidential election, Mr Zuckerberg said a connection is entirely possible.

The US Federal Trade Commission is investigating whether Facebook violated an agreement it signed with the agency in 2011 by its actions in the Cambridge Analytica scandal.

Last week, Mr Zuckerberg threw his support behind proposed legislation, known as the Honest Ads Act that would require social media sites to disclose the identities of buyers of online political campaign ads, but on Tuesday, would not agree to speak out further on behalf of the Honest Ads Act.

Reuters / Newshub.