He figured out a way to hack any of Facebook’s 2 billion accounts, and they paid me a $15,000 bounty for it

[Costas]

https://medium.freecodecamp.org/responsible-disclosure-how-i-could-have-hacked-all-facebook-accounts-f47c0252ae4d

ref - https://www.reddit.com/r/ReverseEngineering/comments/80cjt9/i_figured_out_a_way_to_hack_any_of_facebooks_2/