Facebook Chief Executive Officer Mark Zuckerberg on Tuesday publicly apologised for failing to protect the personal information of millions of people.

Zuckerberg appeared before the United States Senate Judiciary and Commerce Committees after it came to light that the private information of 87 million Facebook users was harvested by the British political consulting firm Cambridge Analytica, which worked on Donald Trump’s presidential campaign.

“We didn’t take a broad enough view of our responsibility, and that was a big mistake,” said Zuckerberg. “It was my mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here.”

Zuckerberg said it was “clearly a mistake” to believe the data-mining company had deleted user data it had harvested in an attempt to sway elections, AP reported. He said Facebook thought the data collection was “a closed case” because it thought the information had been discarded.

In the first of two marathon meetings with the US Senate, Zuckerberg also said Facebook did not alert the Federal Trade Commission, and that the company was prepared to handle the situation differently today.

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Zuckerberg told the senate that his company was “working with” special counsel Robert Mueller in the federal inquiry into alleged Russian interference in the 2016 US presidential campaign. Earlier in the year, Mueller charged 13 Russian individuals and three companies with interfering in the 2016 election through a social media propaganda. A number of the Russian ads were on Facebook.

He said that 2018 was an “important year for the whole world, with several countries like India, Pakistan having elections”. “We’ll do everything possible to ensure these elections are safe,” he said. Facebook wants to protect the integrity of the process and they have deleted thousands accounts that could exploit internet systems and affect elections, he said.

Zuckerberg also told the committees that his company has been alerting some of its users that their data was gathered by Cambridge Analytica.

One of the senators, John Thune from South Dakota, told Zuckerberg that his company had a 14-year history of apologising for “ill-advised decisions” related to user privacy. “How is today’s apology different?” Thune also said there was a need for Facebook to avoid creating “a privacy nightmare”, The New York Times reported.

Zuckerberg responded saying, “We have made a lot of mistakes in running the company. I think it’s pretty much impossible, I believe, to start a company in your dorm room and then grow it to be at the scale that we’re at now without making some mistakes”.

The senators focused on Facebook’s basic functions, such as privacy settings, while also asking Zuckerberg about fake news on the social media platform. They said they are skeptical if the company can regulate itself and indicated putting in place privacy rules.

Zuckerberg said Facebook is now going through “a broader philosophical shift in how we approach our responsibility as a company”, and added that the company needed to take a “more proactive role”.

Following his statements, Facebook shares surged 4.5% for the day, its biggest gain in two years.

On Monday, Zuckerberg admitted to the United States Congress that his social media network did not do enough to prevent the misuse of people’s data.