According to the New York Times and Der Spiegel, the US knew North Korea was behind the Sony Pictures hack because it had secretly infiltrated the country’s computer networks in 2010.
The newspapers cited US officials and leaked documents from the National Security Agency (NSA).
The New York Times said hidden software had alerted US intelligence services to North Korean hacking activity.
North Korea has consistently denied involvement in the security breach.
American investigators believe the hackers spent two months building up a map of Sony’s systems before the hack took place, the papers say.
It also resulted in Sony film The Interview, a comedy about an assassination attempt on North Korean leader Kim Jong-un, being briefly shelved and then released online.
The US Office of the Director of National Intelligence said the intelligence community was fully aware of North Korean attempts to infiltrate US commercial networks, tracking them routinely.
“While no two situations are the same, it is our shared goal to prevent bad actors from exploiting, disrupting or damaging US commercial networks and cyber infrastructure,” said spokesman Brian Hale.
“When it becomes clear that cyber criminals have the ability and intent to do damage, we work cooperatively to defend networks.”
[youtube rajCY7iCjlI 650]