Mark Zuckerberg has admitted Facebook failed to protect user data and prevent manipulation of its platform. Some 87 million users had their personal information harvested for political purposes by Cambridge Analytica.

On the eve of his first congressional hearing, Facebook CEO and founder Mark Zuckerberg admitted that the social network did not do enough to prevent the misuse of user data, placing the blame squarely on himself.

“It’s clear now that we didn’t do enough to prevent these tools from being used for harm …” Zuckerberg said in written testimony released by the US House Energy and Commerce Committee. “That goes for fake news, foreign interference in elections, and hate speech, as well as developers and data privacy.”

The 33-year-old Facebook chief’s testimony was released ahead of the first of two scheduled appearances before congressional committees on Tuesday and Wednesday.

The company is facing the worst privacy crisis in its 14-year history after whistleblowers revealed that the personal information of tens of millions users, mainly in the US, was obtained by political consultancy firm Cambridge Analytica. Facebook itself admitted that the number of affected users is estimated to be around 87 million.

London-based Cambridge Analytica, which counts US President Donald Trump’s election campaign as among its past clients, has disputed the estimated number of affected users.

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

Facebook promises to take necessary steps

Zuckerberg also swore he would take the necessary steps to ensure user data would never again be ill-gotten and misused by an outside party. Other applications, he also noted, were being investigated for their handling of data.