Facebook shares fell 5 percent on Monday, as investors reacted to the social media platform’s involvement in a data scandal.

According to the Observer, Data firm Cambridge Analytica, which collaborated worked with Donald Trump’s election team and the Leave Brexit campaign, harvested the profiles of millions of Facebook’s US voters.

A whisteblower revealed to the publication about how Cambridge Analytica used the personal information of users in early 2014, without authorisation, to facilitate the profiling of individual US voters, for targeted personalised political advertisements.

It has been estimated that as many as 50 million users personal information had been utilised, calling into question how truly accountable social media platforms are in the digital age.

Christopher Wylie, who worked with a Cambridge University academic to obtain the data, told the Observer: “We exploited Facebook to harvest millions of people’s profiles. And built models to exploit what we knew about them and target their inner demons. That was the basis the entire company was built on.

Amid the revelations, both Cambridge Analytica and Facebook are being investigated as part of an inquiry into data and politics by the British Information Commissioner’s Office.

Alongside this, the Electoral Commission is also looking into Cambridge Analytica’s role in the EU referendum.

“We are investigating the circumstances in which Facebook data may have been illegally acquired and used,” commented information commissioner Elizabeth Denham.

“It’s part of our ongoing investigation into the use of data analytics for political purposes which was launched to consider how political parties and campaigns, data analytics companies and social media platforms in the UK are using and analysing people’s personal information to micro-target voters.” She added.

Alongside inquires in the U.K, across the pond, legislators in the U.S are also calling for greater transparency and investigation into the data breach allegations.

“It’s clear these platforms can’t police themselves,” tweeted Senator Amy Klobuchar, a Democratic member of the Senate Judiciary Committee.

Facebook breach: This is a major breach that must be investigated. It’s clear these platforms can’t police themselves. I’ve called for more transparency & accountability for online political ads. They say “trust us.” Mark Zuckerberg needs to testify before Senate Judiciary.

— Amy Klobuchar (@amyklobuchar) March 17, 2018

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Whilst Facebook have dismissed accusations of a ‘data breach’ per se, shares in the company continued to plunge on Monday.

Shares are currently trading -5.84 percent as of 14.43 PM (GMT).