US investigators have concluded that the recent hack of Sony was in fact the result of North Korean hackers.

The Wall Street Journal reported that officials are "still gathering evidence and are trying to build a clearer picture of who directed the hacking and how.”

ABC News further reported that officials believed an elite North Korean hacking unit was behind the attack. The intrusion was traced back through systems including computers in Singapore, Thailand, Italy, Bolivia, Poland, and Cyprus.

The Journal reported that U.S. investigators "strongly suspect" that the attack was carried out by a North Korean government-backed hacking group known as Unit 121, or alternatively as Bureau 121, which is part of the government's General Bureau of Reconnaissance and is believed to have been behind cyberattacks aimed at South Korea.