"I'm really sorry that this happened," the Facebook (FB) CEO told CNN's Laurie Segall in an exclusive TV interview on Wednesday.
News broke this weekend that Cambridge Analytica, a data firm with ties to President Donald Trump's 2016 campaign, accessed information from 50 million Facebook users without their knowledge, and might have kept that data even after Facebook told the company to delete it.
The revelation put Facebook and Zuckerberg under the microscope for their handling of user data and privacy.
Zuckerberg addressed the scandal publicly through a Facebook post on Wednesday. He wrote that the company made "mistakes" and outlined how it has changed its policies to make sure that user data is protected.
"I wish we'd taken those steps earlier," Zuckerberg told Segall. "That ... is probably the biggest mistake that we made here."
In 2014, Facebook changed its platform to limit the amount of data that third-party developers could access.
Aleksandr Kogan, the data scientist who passed along data to SCL Group and its affiliate Cambridge Analytica, built a Facebook app that drew data from users and their friends in 2013. He was allowed access to a broad range of data at the time.
Though Kogan's data was properly obtained, he breached Facebook's policy when he shared that information with a third party, Facebook has said. When Facebook learned about the information being shared, it asked Cambridge Analytica to destroy the data. Cambridge said it had.
But a former contractor, Christopher Wylie, disputes that Cambridge Analytica destroyed the user data.