Facebook has discovered a massive security breach affecting 50 million user accounts - including those of Facebook boss Mark Zuckerberg and COO Sheryl Sandberg.

The social media giant said attackers exploited the site's 'View As' feature, which lets people see what their profiles look like to other users.

The unknown attackers took advantage of a feature in the code called 'Access Tokens,' to take over people's accounts, potentially giving hackers access to private messages, photos and posts - although Facebook said there was no evidence that had been done.