The American secret service NSA was able to access to sensitive North Korean systems since 2010. Information gathered by espionage software on these systems led to the conclusion that North Korea is behind the Sony hack, according to The New York Times.
The American secret service would have decided to penetrate Chinese networks which connect North Korea with the rest of world in 2010. Together with South Korea and some other partner countries, the NSA would have been able to track internet connections frequently used by North Korean hackers. The United States would have taken action because the country was worried about increasing cyberwarfare capabilities of North Korea.
The NSA would have succeeded to smuggle malware inside networks used by North Korean hackers. A team of hackers in the communist country would operate by the name Bureau 121 which in its turn was under control of the secret service of the Asian country. According to South Korea the team of hackers consists of 6,000 people.
The data the NSA gathered using the malware would have been used to convince President Obama that North Korea is behind the hack on Sony pictures, according to The New York Times which claims it received information from government employees and computer experts. Also German publication Der Spiegel published a new NSA document which underlines the information.
President Obama would have no doubt that North Korea is behind the Sony hack. The United States have initiated economical sanctions against the country due to the incident.
