The US government has taken a lot of heat for publically blaming North Korea for the hack on Sony Pictures last November. Up to this point, however, they haven't provided many details as to what led them to that conclusion - until now. According to FBI director James Comey, the Sony hackers slipped up on more than one occasion by failing to use proxy servers to mask the origin of their attack. This move revealed IP addresses that the FBI claims were used exclusively by North Korea.