Facebook CEO Mark Zuckerberg acknowledged Wednesday the social media company erred and vowed to protect users’ data after it was revealed Cambridge Analytica, a British data firm, improperly harvested and misused data from 50 million Facebook profiles.

“We have a responsibility to protect your data, and if we can’t then we don’t deserve to serve you,” Zuckerberg wrote on his Facebook page. “I’ve been working to understand exactly what happened and how to make sure this doesn’t happen again.