North Korean students use different colored signs to form a picture of a child in uniform as a background during a mass gymnastic and artistic performance in Pyongyang on July 26, 2013. Reuters/Jason Lee

North Korea’s Internet links were restored late Monday after hours of complete outage, a report said, citing a U.S. company that monitors Internet infrastructure. The East Asian country, currently at the center of a heated feud with the United States over the hacking of Sony Pictures Entertainment last month, faced the outage days after the U.S. said it would “respond proportionately” to an alleged Pyongyang-backed hack of the studio's systems.

Pyongyang has been accused of aiding the hack against Sony Pictures in protest of the studio's comedy movie “The Interview,” which revolves around a plot to assassinate North Korean leader Kim Jong Un. Dyn Research, a New Hampshire-based Internet performance company, said the reason for North Korea’s Internet outage is still not known but added that a hacking attack could not be ruled out.

“We’ve yet to see how stable the new connection is. The question for the next few hours is whether it will return to the unstable fluctuations we saw before the outage,” Jim Cowie, chief scientist at Dyn Research, told Reuters, adding that North Korea's Internet links were unstable on Monday, before the country went completely offline.

Except for some satellite links, almost all of North Korea’s Internet links and traffic pass through China, and very few of the country’s 24 million people can access the Internet.

“North Korea has significantly less Internet to lose, compared to other countries with similar populations: Yemen (47 networks), Afghanistan (370 networks), or Taiwan (5,030 networks),” Dyn Research said in a report. “And unlike these countries, North Korea maintains dependence on a single international provider, China Unicom. That’s a fragile state of affairs.”

Technical Snag Or Hack?

“There's either a benign explanation -- their routers are perhaps having a software glitch; that’s possible. It also seems possible that somebody can be directing some sort of an attack against them and they're having trouble staying online,” Doug Madory, director of Internet analysis at Dyn Research, told Reuters.

According to other experts, North Korea's Internet connection was likely attacked by hackers using a botnet, which is a group of infected computers that can be controlled remotely.

“It would be possible that a patriotic actor could achieve the same results with a botnet, however the President promised a proportional response,” Tom Kellermann, chief cybersecurity officer at Trend Micro, a California-based security software company, was quoted by Reuters as saying.

Is The U.S. Responsible?

President Barack Obama had vowed to take action against Pyongyang only days before and the timing of the Internet outage in North Korea points to a potential involvement of the U.S. However, a set of traffic monitoring data has suggested that the U.S. is probably not behind North Korea’s Internet problems.

According to data provided by Massachusetts-based Arbor Networks, the denial-of-service (DoS) attacks against North Korea had already begun before Obama pledged a proportionate response to the hacking of Sony Pictures. The data also revealed that the first sign of an attack on North Korea’s Internet infrastructure was found on Dec. 18, one day before the FBI formally confirmed North Korea’s involvement, The Verge reported.

“I’m quite sure that this is not the work of the U.S. government. Much like a real world strike from the U.S., you probably wouldn’t know about it until it was too late,” Dan Holden, a cybersecurity expert at Arbor Networks, said in a statement. “This is not the modus operandi of any government work.”