Facebook has seen a number of legal troubles in recent days, from gender bias claims over advertising practices to content moderators alleging they were traumatized by graphic images. But on Friday, the company announced what could blossom into its biggest legal issue to date: a data breach that affects more than 50 million users.

On a post on the company’s blog, authored by Facebook vice president of product management Guy Rosen, the social network announced that it had discovered a security breach affecting almost 50 million accounts on Tuesday, Sept. 25. Facebook said it has already fixed the vulnerability and informed law enforcement of the issue.