A Facebook breach has compromised almost 50 million accounts. After discovering the breach on September 25, the company reset the access tokens of the 50 million affected accounts and 40 million others as a precautionary step. The attackers accessed the accounts via a vulnerability involving Facebook's access tokens which keep users logged in.
https://www.notebookcheck.net/50-million-Facebook-accounts-were-compromised-due-to-a-security-flaw.336472.0.html