Mark Zuckerberg, the co-founder and CEO of Facebook, appeared before the Senate Judiciary and Commerce Committee yesterday for the first of two US congressional hearings in the wake of the Cambridge Analytica scandal. During almost five hours of questioning by 44 US Senators, Zuckerberg repeated apologies he previously made for a range of problems that have beset his social network, from a lack of data protection, to Russian agents using Facebook to influence US elections. However, the 33-year-old multi-billionaire was a little reluctant to speak when the issue of tracking users across the web arose. Facebook's CEO was asked by Sen. Roger Wicker whether or not rumours the California-based company tracks user activity around the web even when they have logged out of the service were true. "There have been reports that Facebook can tracks a user's internet browsing activity even after that user has logged off of the Facebook platform," Senator Wicker said. "Can you confirm whether or not this is true?" It’s perfectly possible for Facebook to track non-users and logged-out users via social plugins and cookies found across websites around the web. Researchers determined the practice was occurring back in 2015, stating that ”Facebook users who are logged-out from Facebook are still being tracked through the social plug-ins."

FACEBOOK • GETTY Facebook CEO Mark Zuckerberg fielded questions for close to five hours

In February 2018, a Belgium court looked into this practice and ruled it was illegal. However, Mark Zuckerberg didn’t want to address the practice in the Senate Judiciary and Commerce Committee. "Senator, I want to make sure I get this accurate so it would probably be better to have my team follow up afterwards," he replied. "You don't know?” quizzed Senator Wicker. "I know that people use cookies on the internet, and that you can probably correlate activity between, ermm, between sessions," Mark Zuckerberg responded. "We do that for a number of reasons, including security and including measuring ads to make sure that the ad experiences are the most effective." According to the man behind Facebook, the technology company correlates activity between users sessions.

GETTY Facebook CEO Mark Zuckerberg was called to testify following the Cambridge Analytica scandal

However, Zuckerberg fell short of explaining exactly what that meant, and how much data is extrapolated from this process. Still, investors were suitably impressed with Zuckerberg during the hearing. Shares in Facebook posted their biggest daily gain in nearly two years, closing up 4.5 per cent – and adding a few billion dollars to the 33-year-old Facebook CEO’s personal wealth. Facebook shares fell steeply last month 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. Wearing a dark suit and tie instead of his typical T-shirt and jeans, Zuckerberg remained largely unruffled and serious as senators questioned him. But some senators did provoke a reaction. Zuckerberg 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. But the senators who asked sharp questions were often at a disadvantage because each had only five minutes to pin down the billionaire. Democratic Senator Kamala Harris, from Facebook's home state of California, asked a line of questions about whether Zuckerberg or his senior executives considered notifying Facebook users of the data breach. She was among the lawmakers dissatisfied. "Mark Zuckerberg's failure to answer several critical questions during his appearance before the Senate today leaves me concerned about how much Facebook values trust and transparency," she later wrote on Twitter.

Facebook in pictures Mon, September 28, 2015 We look at the social networking phenomena Facebook in pictures Play slideshow ASSOCIATED PRESS 1 of 10 Facebook founder Mark Zuckerberg speaks in the Galileo Auditorium on Microsoft’s Silicon Valley Campus in Mountain View, Wednesday, Oct. 13, 2010