The attack occurred when a handful of Facebook employees visited a developer’s compromised website, which led to malware being installed on their laptops. No user information was compromised during the attack. Reports say Facebook knew about the attacks, which likely exploited a zero-day Java software flaw, well before the announcement. Twitter social network said earlier this month that it had been hacked, and that approximately 2,50,000 user accounts were potentially compromised, with attackers gaining access to information including user names and email addresses.
Source: https://thehackernews.com/2013/02/facebook-hacked-in-zero-day-attack.html