Facebook under pressure as US and EU urge probe of data practices

Officials have called for investigations into media reports that political analytics firm Cambridge Analytica harvested the private data on more than 50 million Facebook users

Facebook Chief Executive Mark Zuckerberg is facing calls to explain how a consultancy that worked on US President Donald Trump's election campaign gained improper access to data on 50 million Facebook users.

Facebook's shares closed down nearly 7% today, wiping nearly $40 billion off its market value as investors worried that new legislation could damage the company's advertising business.

Officials in the United States, Britain and Europe have called for investigations into media reports that political analytics firm Cambridge Analytica harvested the private data on more than 50 million Facebook users to develop techniques to support Mr Trump's 2016 presidential election campaign.

The scrutiny presents a fresh threat to Facebook's reputation, which is already under attack over Russia's alleged use of Facebook tools to sway US voters with divisive and false news posts before and after the 2016 election.

Facebook today said it had hired digital forensics firm Stroz Friedberg to carry out a comprehensive audit of Cambridge Analytica, which had agreed to comply and give the forensics firm complete access to their servers and systems.

Cambridge Analytica said it strongly denies the media claims, and that it deleted all Facebook data it obtained from a third-party app in 2014 after learning the information did not adhere to data protection rules.

But further allegations about the firm's tactics have piled up, as Channel 4 News published a video of Cambridge Analytica executives talking about using bribes, former spies and Ukrainian sex workers to entrap politicians.

Facebook was already facing calls on Saturday for regulation from US Congress and questions about personal data safeguards after reports in the New York Times and London's Observer over the weekend.

Mr Zuckerberg is facing calls to testify before Congress, and has received letters asking about company policies for sharing user data with third parties.

Facebook usually sends lawyers to testify to Congress, or allows trade organisations to represent it and other technology companies.

Facebook has taken voluntary steps to restrict possible foreign interference and combat false news, but they have not been forced by law or regulation to make changes and legislation on the issue has stalled.

It was not clear whether Republicans who hold congressional committee gavels would announce hearings related to Facebook and Cambridge Analytica.

Some technology lobbyists have begun to quietly acknowledge the era of a hands-off approach to Silicon Valley from US policymakers may be fading.

Facebook said on Friday it had learned in 2015 that a Cambridge University psychology professor lied to the company and violated its policies by passing data to Cambridge Analytica from a psychology testing app he had built.

Facebook said it suspended the firms and researchers involved. It also said the data had been misused but not stolen, because users gave permission.

European officials, who have been more willing to regulate Silicon Valley companies than their US counterparts, were especially strident in criticism of Facebook.

The revelations about Cambridge Analytica were "horrifying, if confirmed," said EU Justice Commissioner Vera Jourova. "We don't want this in the EU and will take all possible legal measures" including stricter rules under the bloc's General Data Protection Regulation that takes effect in May, she said.

A spokesman for British Prime Minister Theresa May said the allegations were "clearly very concerning."