He said: "We’re going to be investigating many apps, tens of thousands of apps. And if we find any suspicious activity we’re going to conduct a full audit of those apps to understand how they’re using their data and if they’re doing anything improper."

In a public apology Mr Zuckerberg added: "We have made a lot of mistakes in running the company. It's pretty impossible to start a company in your dorm room and grow to that size and and not make mistakes.

"We're going through a broad philosophical shift in how we view the company. What we've learned now, whether it's data privacy or 'fake news' is we need to take a more proactive role. It's our responsibility. It's not enough to just build tools, we have to make sure they are used for good. People will measure us by our results on this. I'm committed to getting this right."

Mr Zuckerberg said there would "always be a free version of Facebook" amid controversy over its business model of raising money from adverts.

Regulation

Mr Zuckerberg indicated he was open to some kind of regulation.

Appearing to embrace European-style regulation, he pointed to Europe where there are tighter rules on companies harvesting and marketing user data.

"I think they get things right," he said. "My position is not that there should be no regulation. I think the real question as the internet becomes more important in people's lives is what is the right regulation."

Regulators in the European Union are tougher with companies like Facebook in how they handle users' data. Under the General Data Protection Regulation, which comes into effect in May, companies have to give customers much greater control over their data. Companies like Facebook could face heavy fines of up to four per cent of global revenues if they break the law.

'Your user agreement sucks'

The senators bombarded Mr Zuckerberg with questions about an array of Facebook's lengthy privacy policy and data, but didn't always seem to know how to follow up the tech billionaire's talk of algorithms and AI systems. So one member of the joint committee, average age 62, got to the point.

"I just don't feel like we're connecting," Senator John Kennedy, told Mr Zuckerberg in hour four of the hearing. "Your user agreement sucks."