Facebook revealed that an attack on its computer network - the biggest in the company's history - exposed the personal information of nearly 50 million users.

Facebook’s code was exploited by hackers who gained access to user accounts, as well as apps like Spotify, Instagram, and others that are directly connected to Facebook. “We’re taking it really seriously,” founder and chief executive Mark Zuckerberg  said in a conference call with various reporters. “I’m glad we found this, but it definitely is an issue that this happened in the first place.”

Even the accounts of executives Zuckerberg and Sheryl Sandberg were affected via three software flaws in Facebook’s systems. According to Facebook, these attackers had gained access through bugs in the site’s “View As” feature, which allows Facebook users to monitor what information other people can see about them.

Recommended precautions include changing your password and turning on two-factor authentication. Facebook itself outlined the security breach in an update post.

In other Facebook news, read about how Instagram co-founders resigned from Facebook after alleged disputes with Mark Zuckerberg.