Facebook has announced that 50 million accounts may have been breached. While Facebook does not currently know whether any personal data had been accessed by hackers, or if the breach allowed hackers to take over accounts, Facebook does acknowledge that it is possible and that it is looking into it.
Breach announced: September 28, 2018
Description of the breach: On September 28, Facebook publicly acknowledged that nearly 50 million user accounts had been compromised. While it is not currently known who accessed, or to what extent user data was compromised, Facebook is continuing to investigate. In the meantime, to safeguard user accounts facebook has reset 90 million user accounts which will require these users to log back into their accounts.
Data breach period: Prior to August 20, 2018
Facebook Newsroom security update: Link