Cloud-based DNS company Dyn said North Korea's Internet links with the rest of the world were unstable on Monday before going offline completely. The links were restored a few hours later.
Dyn said the cause is not yet known, but said it could be something benign like a technological glitch with the routers, or it could be something malicious like a hacking attack, saying "It also seems possible that somebody can be directing some sort of an attack against them."
The White House previously said the cyber attack on Sony, which was blamed on North Korea, was a serious national security matter and it was considering a proportional response. However, Several US officials said the US government was not involved in any cyber action against North Korea.
The hackers, calling themselves "Guardians of Peace," stole data from Sony, then demanded the movie, The Interview, be withdrawn because it features a plot to assassinate North Korean leader Kim Jong-Un. Sony caved after the personal details of employees were leaked amongst other data.