People responsible for the hack are so-called white hat hackers from the OurMine group. The group has made it inside both of Facebook’s accounts, but it did not use its access to do anything bad; instead, the hackers have left behind a message inviting FB to talk to them about improving their security.
This is not the first time OurMine has done something like that. They have hacked a number of companies in the past, including HBO and BuzzFeed, always just to let them know that they ought to improve their e-security. Very nice of them, but i wish they would save this effort for companies that are more worthy of help.