North Korean websites have sprung back online after being offline for nearly ten hours. At one point during the outage the entire country was offline.

Barack Obama had promised a "proportional response" against North Korea in the wake of allegations that it is responsible for the devastating cyberattack on Sony Pictures that has resulted in thousands of leaked emails and the cancellation of the James Franco film The Interview. Is this the retaliation? The US government refused to comment.

The country already has weak links to the internet, but some computer experts described this as one of the worst shutdowns in recent years and one said the type of system failure was consistent with an attack.

Doug Madory, director of internet analysis at Dyn Research, told CNN during the failure: "Usually there are isolated blips, not continuous connectivity problems. I wouldn't be surprised if they are absorbing some sort of attack presently".

However, the president of CloudFlare speculated that it was more likely to be the work of a teenage hacktivist. "If it is an attack, it's highly unlikely it's the United States. More likely it's a 15-year-old in a Guy Fawkes mask," he said.

The US government's refusal to confirm or deny involvement in the cyberattack mirrors the North Koreans praise of the hacking collective Guardians Of Peace who wrought havoc on Sony, the studio responsible for releasing The Interview, a film about Kim Jong-un's assassination.

At the time, North Korea denied involvement while heaping praise on the attackers. Now, US are deflecting questions using similar tactics. Marie Harf from the National Security Council refused to discuss "operational details" with CNN.

"We aren't going to discuss, you know, publicly, operational details about the possible response options or comment on those kind of reports in any way, except to say that as we implement our responses, some will be seen, some may not be seen".

Is this the beginning of a cold cyber war?