Facebook founder Mark Zuckerberg on Wednesday admitted to mistakes that led to the private data of more than five crore users of the social networking site allegedly being used for United States President Donald Trump’s political campaign in 2016. A British firm, Cambridge Analytica, is at the centre of the scandal and is accused of using the data on behalf of political clients.

“We have a responsibility to protect your data, and if we can’t, then we don’t deserve to serve you,” Zuckerberg said in a post on his Facebook page. He pledged to take measures to protect user data and make it harder for apps to harvest user information.

Zuckerberg gave a detailed timeline of the events that led to the “breach of trust”. He said a psychology professor at the University of Cambridge, Aleksandr Kogan, had in 2013 built an app, which was installed by 3,00,000 users, who shared their data as well as some of their friends’ data. In 2015, he said, Facebook learnt that Kogan had passed on data from an app that he had created to Cambridge Analytica. He said Kogan and Cambridge Analytica had at that time certified that they had deleted all improperly acquired data.

Zuckerberg has now pledged to investigate all Facebook apps that had access to user data before the guidelines on data access was changed in 2014. He also said the company would conduct a full audit of all apps to investigate any suspicious activity. Facebook said it will restrict developers’ data access even further in future.

“While this specific issue involving Cambridge Analytica should no longer happen with new apps today, that doesn’t change what happened in the past,” Facebook’s chief executive officer said. “We will learn from this experience to secure our platform further and make our community safer for everyone going forward.”

‘It was a mistake to trust Cambridge Analytica’

Politicians in the United States have called for Zuckerberg to testify before the Congress in wake of the data breach scandal. “What we try to do is send the person at Facebook who will have the most knowledge,” Zuckerberg said in an interview on CNN. “If that’s me, then I am happy to go.”

He said the company will reach out to each and every user whose data might have been affected. “I think that this was clearly a mistake in retrospect,” Zuckerberg said in the interview. “We need to make sure we don’t make that mistake ever again.”

Apart from using private data of millions of people, Cambridge Analytica is also accused of using shell companies, sex workers, fake news and bribes to sway election outcomes in several countries, according to a report by Channel4News. These claims were purportedly made by top executives to the channel’s undercover reporters.

The channel also claims to have evidence of the firm’s officials boasting about having worked in election campaigns across the world, including India. However, the report does not clarify which Indian political party was engaged with the firm.

‘Facebook committed to checking interference in Indian polls’

In an interview to CNN on Wednesday, Zuckerberg said Facebook was committed to doing everything to ensure that the integrity of elections in India and other places are secured on the social networking site.

“There’s a lot of hard work that we need to do to make it harder for nation-states like Russia to do election interference, to make it so that trolls and other folks can’t spread fake news, but we can get in front of this,” said Zuckerberg. “And we have a responsibility to do this, not only for the 2018 midterms in the US, which are going to be a huge deal this year and that’s just a huge focus for us but there’s a big election in India this year, there’s a big election in Brazil, there are big elections around the world, and you can bet that we are really committed to doing everything that we need to to make sure that the integrity of those elections on Facebook is secured.”