By Bartholomew Madukwe with Agency Report

Chief Executive of Facebook Inc, Mark Zuckerberg, will testify about data leak of 50 million Facebook users, next Tuesday and Wednesday, during two U.S. congressional hearings.

The previous estimate of more than 50 million Facebook users affected by the data leak came from two newspapers, the New York Times and London’s Observer, based on their investigations of Cambridge Analytica, reports Reuters.

In a conference call with reporters, Zuckerberg said the personal information of up to 87 million users, mostly in the United States, may have been improperly shared with political consultancy Cambridge Analytica, up from a previous news media estimate of more than 50 million.

Zuckerberg told reporters that he accepted blame for the data leak, which has angered users, advertisers and lawmakers.

“When you’re building something like Facebook that is unprecedented in the world, there are going to be things that you mess up; the important thing was to learn from mistakes,” he said.

About him stepping down, Zuckerberg said he was not aware of such discussions on the Facebook board, noting that although directors would face a challenge if they wanted to oust him because he is the controlling shareholder.

The Chief Executive hinted that he had not fired anyone over the scandal and did not plan to, saying “I’m not looking to throw anyone else under the bus for mistakes that we made here”.

Facebook first acknowledged last month that personal information about millions of users wrongly ended up in the hands of Cambridge Analytica, which counted U.S. President Donald Trump’s 2016 campaign.

Cambridge Analytica (CA) is a British political consulting firm which combines data mining, data brokerage, and data analysis with strategic communication.

“Facebook should have done more to audit and oversee third-party app developers like the one that Cambridge Analytica hired in 2014. Knowing what I know today, clearly we should have done more.

Facebook was taking steps to restrict which personal data is available to third-party app developers. It might take two more years to fix Facebook’s problems,” he said.

Facebook Chief Technology Officer, Mike Schroepfer, wrote in a blog post that most of the up to 87 million people whose data was shared with Cambridge Analytica were in the United States.

Shares in Facebook closed down 0.6 percent on Wednesday to $155.10. They have tumbled more than 16 percent since the Cambridge Analytica scandal broke, says Reuters.

Meanwhile, the Nigeria’s government has commenced an investigation into the recent revelation that ahead of the 2015 general elections, a Nigerian billionaire and supporter of former President Goodluck Jonathan paid £2m to Cambridge Analytica, to hack into the medical records of President Muhammadu Buhari, candidate of the All Progressives Congress (APC).

It was gathered that the government is also probing the report which suggested that the consulting firm that combines data mining, brokerage and analysis with strategic communications for electoral process manipulated Nigeria’s 2007 elections by organising campaigns to weaken the chances of opposition parties.