https://motherboard.vice.com/en_us/article/qvy9k7/facebook-hundreds-of-millions-user-passwords-plaintext-data-leak

Facebook confirmed on Thursday that it had kept “hundreds of millions” of user passwords in a “readable format”—meaning engineers and other employees with access to the company’s internal systems could see the actual plaintext passwords.

In a press release, the social network said that it discovered the misshap during a “routine security review in January.” News of the mistake was first reported by independent security journalist Brian Krebs.