In planned testimony for his Wednesday hearing with the House Energy and Commerce Committee, Facebook CEO Zuckerberg acknowledged that Facebook did not go far enough in its efforts to curb foreign influence, eliminate fake news, and protect users’ privacy. He will testify before Congress over two days this week.

“We didn’t take a broad enough view of our responsibility, and that was a big mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here,” he wrote in the planned testimony, which was released on Monday ahead of his appearances.

Zuckerberg confirmed in the testimony that the Internet Research Agency (IRA), a Russian troll farm, reached an estimated 126 million people with its Facebook content in two years and an additional 20 million through Instagram. The IRA also purchased ads on Facebook, which were seen by about 11 million people in the U.S., according to Zuckerberg. He wrote in the testimony that Facebook shut down the IRA’s accounts in August 2017.

Facebook has already begun rolling out initiatives to prevent abuse on such a wide scale in the future, including changes to its advertising policy and new security technologies.

Zuckerberg also addressed Cambridge Analytica, the British data firm that worked for President Donald Trump’s campaign and collected Facebook user data through a personality quiz. He wrote in his testimony that Facebook will make it easier for users to remove applications that collect their personal data.

Read Zuckerberg’s planned testimony: