What is Zuckerberg doing to make sure the Cambridge Analytica episode never happens again?

Facebook is doing a full audit of Cambridge Analytica's system to make sure they have deleted all information.

They're restricting the amount of access to information that app developers will have going forward. In 2014, Facebook made large changes to restrict access on the platform. "Clearly, we did not do that soon enough," he says. "If we'd done that earlier, perhaps we wouldn't be here today."

Security staff increased from 15,000 to 20,000.

Facebook is auditing all third party apps.

Senator Jon Tester says he doubts Facebook can do a proper audit of Cambridge Analytica because some of their records are overseas in the UK.