[jammygit]

Facebook likes their interview nonsense, but stores passwords in plaintext. I think the credibility of the system is in question

[jensvdh]

They didn't store pw in plain text. Pw were accidentally captured in logs and those logs were stored in an internal DB. This happens often.

[chopin]

That's storing passwords in plain text. "Happens often" is no valid excuse, on the contrary. If it happens often you should know about it if you are a qualified engineer.