N. Korea loses Internet for 9 hours

NEW: Cybersecurity expert: North Korea "may have disconnected themselves"

Research company says North Korea's Internet goes back down, only to return

Monday's Web blackout lasted more than nine hours, according to Dyn Research

Web disruption came amid escalating war of words between the U.S., North Korea

(CNN) -- North Koreans' ability to surf the Internet -- for the few in the isolated nation who could ever really go online anyway -- is rockier than ever.

Dyn Research reported on Monday that the country's Internet was down, after 24 hours of "increasing instability." It stayed dead for more than nine hours, then came back to life -- but not for long. Half a day later Dyn said it was down again. Then it was back up, at about 1 a.m. Wednesday Pyongyang time (11 a.m. Tuesday ET), the company said.

But the assessment of Dyn, a company that monitors Internet performance worldwide, made earlier Tuesday, did not change: "North Korea continues its struggles to stay online."

The timing of North Korea's latest Internet issues makes them significant. They come days after the U.S. government blamed Pyongyang for being behind the hacking of Sony Pictures over that company's production of "The Interview" -- a comedy depicting the assassination of North Korean leader Kim Jong Un -- as well as threats against anyone who dared watch the movie.

Making fun of Kim is 'path to death'

Experts: N. Korea's Internet disrupted

What are military options for N. Korea?

Reports: North Korea's Internet is down

North Korea denied any responsibility, even as it blamed the U.S. government for being behind the making of the Seth Rogen-James Franco film. Its totalitarian government went on to officially make its own threat, warning the United States that its "citadels" will be attacked, dwarfing the hacking attack on Sony.

Pyongyang hasn't leveled any blame or threats about its latest Internet outage. But experts are skeptical that the American government had any involvement.

That's almost irrelevant, said Mike Chinoy, a frequent traveler to North Korea and former CNN correspondent.

"The issue ... is not whether it was or it wasn't (the United States that knocked out North Korea's Internet). The issue is what the North Koreans think it was," said Chinoy, a U.S.-China Institute senior fellow.

"And I think it's safe to assume -- unless they themselves took their system offline for their own security, which is not impossible -- they'll be looking to respond."

Cyber conflict with North Korea is 'dangerous uncharted territory'

Expert: Could be 'a 15-year-old in a Guy Fawkes mask'

So who is behind North Korea's Internet problems?

Unlike the Sony cyberattack and threats, which were linked to a group called "Guardians of Peace," the latest issues haven't been tied to any group or government.

It's possible they have nothing to do with the Sony dust-up and are simply an internal matter. Another possibility: North Korea's Internet traffic is routed through China, so issues or officials there may be to blame.

Another option: it could be a deliberate move by the country's own government.

"North Korea may have disconnected themselves, either preemptively to prevent that movie from being distributed, but also, probably more likely, in a defensive posture," said Shawn Henry, a cybersecurity expert and former executive assistant director of the FBI.

Talking when North Korea's Internet was totally down, Dyn Research's Doug Madory said "usually there are isolated blips" anyway in the country's service. But he thinks what happened here was different.

"I wouldn't be surprised if they are absorbing some sort of attack," Madory said.

In an undated photo released on November 28, North Korea leader Kim Jong Un is seen on a field trip to see the airwomen of the KPA Air and Anti-Air Force. North Korean Newspaper Rodong Sinmun reported Kim "guided a flight drill of pursuit airwomen of the KPA Air and Anti-Air Force. He went out to an airport's runway to learn about the plan for solo take-off and landing drill by women pilots of pursuit planes and guide their flight."

A picture released by the North Korean Central News Agency shows Kim appearing without his cane at an event with military commanders in Pyongyang on Tuesday, November 4. Kim, who recently disappeared from public view for about six weeks, had a cyst removed from his right ankle, a lawmaker told CNN.

Kim is seen walking with a cane in this image released Thursday, October 30, by the state-run Korean Central News Agency.

Kim talks with officials during an airmen inspection.

Kim sits in the pilot's seat of a fighter jet during the inspection.

Kim sits at a desk during the inspection.

This undated photo, released Tuesday, October 14, by the KCNA, shows Kim inspecting a housing complex in Pyongyang, North Korea. International speculation about Kim went into overdrive after he failed to attend events on Friday, October 10, the 65th anniversary of the Workers' Party. He hadn't been seen in public since he reportedly attended a concert with his wife on September 3.

A picture released by the KCNA shows Kim and his wife watching a performance by the Moranbong Band on Wednesday, September 3, in Pyongyang.

Kim tours a front-line military unit in this image released Wednesday, July 16, by the KCNA.

Kim poses for a photo as he oversees a tactical rocket-firing drill in June.

Kim watches a tactical rocket-firing drill in June.

A North Korean soldier patrols the bank of the Yalu River, which separates the North Korean town of Sinuiju from the Chinese border town of Dandong, on Saturday, April 26.

A soldier looks through binoculars inside a sentry post along the bank of the Yalu River on Monday, April 7.

In this photo released Thursday, April 24, by the Korean Central News Agency, Kim smiles with female soldiers after inspecting a rocket-launching drill at an undisclosed location.

A picture released Tuesday, March 18, by the KCNA shows Kim attending a shooting practice at a military academy in Pyongyang.

A North Korean soldier uses binoculars on Thursday, February 6, to look at South Korea from the border village of Panmunjom, which has separated the two Koreas since the Korean War.

A North Korean soldier kicks a pole along the banks of the Yalu River on Tuesday, February 4.

A photo released by the KCNA on Thursday, January 23, shows the North Korean leader inspecting an army unit during a winter drill.

Kim inspects the command of an army unit in this undated photo released Sunday, January 12, by the KCNA.

Kim visits an army unit in this undated photo.

A picture released by the KCNA on Wednesday, December 25, shows Kim visiting an army unit near the western port city of Nampo.

Kim inspects a military factory in this undated picture released by the KCNA in May 2013.

Kim visits the Ministry of People's Security in 2013 as part of the country's May Day celebrations.

A North Korean soldier, near Sinuiju, gestures to stop photographers from taking photos in April 2013.

North Korean soldiers gather by the docks in Sinuiju, near the Chinese border, in April 2013.

North Korean soldiers patrol near the Yalu River in April 2013.

Kim is briefed by his generals in this undated photo. On the wall is a map titled "Plan for the strategic forces to target mainland U.S."

Kim works during a briefing in this undated photo.

In this KCNA photo, Kim inspects naval drills at an undisclosed location on North Korea's east coast in March 2013.

Kim, with North Korean soldiers, makes his way to an observation post in March 2013.

Kim uses a pair of binoculars to look south from the Jangjae Islet Defense Detachment, near South Korea's Taeyonphyong Island, in March 2013.

Kim is greeted by a soldier's family as he inspects the Jangjae Islet Defense Detachment in March 2013.

Kim is surrounded by soldiers during a visit to the Mu Islet Hero Defense Detachment, also near Taeyonphyong Island, in March 2013.

Kim arrives at Jangjae Islet by boat to meet with soldiers of the Jangjae Islet Defense Detachment in March 2013.

Soldiers in the North Korean army train at an undisclosed location in March 2013.

In a photo released by the official North Korean news agency in December 2012, Kim celebrates a rocket's launch with staff from the satellite control center in Pyongyang.

Kim, center, poses in this undated picture released by North Korea's official news agency in November 2012.

Kim visits the Rungna People's Pleasure Ground, under construction in Pyongyang, in a photo released in July 2012 by the KCNA.

A crowd watches as statues of North Korean founder Kim Il Sung and his son Kim Jong Il are unveiled during a ceremony in Pyongyang in April 2012.

A North Korean soldier stands guard in front of an UNHA III rocket at the Tangachai-ri Space Center in April 2012.

In April 2012, Pyongyang launched a long-range rocket that broke apart and fell into the sea. Here, the UNHA III rocket is pictured on its launch pad in Tang Chung Ri, North Korea.

A closer look at the UNHA III rocket on its launch pad in Tang Chung Ri, North Korea.

A military vehicle participates in a parade in Pyongyang in April 2012.

North Koreans wave flags in front of portraits of Kim Il Sung, left, and Kim Jong Il during celebrations to mark the 100th birth anniversary of Kim Il Sung in Pyongyang in April 2012.

North Korean soldiers relax at the end of an official ceremony attended by leader Kim Jong Un at a stadium in Pyongyang in April 2012.

Kim Jong Un applauds as he watches a military parade in Pyongyang in April 2012.

A North Korean soldier stands on a balcony in Pyongyang in April 2012.

North Korean soldiers march during a military parade in Pyongyang in April 2012.

Soldiers board a bus outside a theater in Pyongyang in April 2012.

North Korean performers sit below a screen showing images of leader Kim Jong Un in Pyongyang in April 2012.

North Korean soldiers salute during a military parade in Pyongyang in April 2012.

North Korean soldiers listen to a speech during an official ceremony attended by leader Kim Jong Un at a stadium in Pyongyang in April 2012.

Members of a North Korean military band gather following an official ceremony at the Kim Il Sung stadium in Pyongyang in April 2012.

North Korean military personnel watch a performance in Pyongyang in April 2012.

A North Korean controller is seen along the railway line between the Pyongyang and North Pyongan provinces in April 2012.

A North Korean military honor guard stands at attention at Pyongyang's airport in May 2001.

Kim Jong Un and North Korea's military

$Photos: Kim Jong Un\'s military$ Photos: Kim Jong Un's military

New North Korea threats to attack U.S.

U.S. State Department spokeswoman Marie Harf deflected a question about the disruption. "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," she said.

No one is saying the U.S. government couldn't have carried out such an attack. But tech experts say it might not have needed to, given the ability of anyone, anywhere to do something like this.

What happened with Sony, especially the studio's decision to shelve -- at least temporarily -- the release of "The Interview," got a lot of people upset.

Matthew Prince, president of the performance and security company CloudFlare, told CNN he couldn't say definitively that there was an attack at all. But if there was, he said it's possible a lone individual, not an entire government, was behind it.

"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," said Prince, tying the prospective attackers to those connected to or inspired by the hacktivist movement Anonymous.

Limited technology, but not when it comes to hacking

Do these outages equal outrage, leaving North Koreans unable to view "Gangnam Style" for the 2-billionth-plus time? Have they been frustrated when they tried to check on the latest NBA results for their fantasy teams or engage in heated debates about local, national and international politics?

No. There's a reason the Committee to Protect Journalists ranks North Korea second on its list of "Most Censored Countries." Only a smattering of "ruling elites" can go online freely, leaving the public limited to a "heavily monitored and censored (intranet) network with no connections to the outside world," according to the advocacy group.

Widespread computer technology overall isn't a reality in one of the world's poorest and, according to many outsiders, most antiquated countries.

New North Korea threats to attack U.S.

Defector: N. Korea running hacker network

North Korea slams U.S. government

Hacking: Did we underestimate N. Korea?

A 2012 report from KISA, South Korea's Internet development agency, noted North Korea then had only 1,024 IP addresses -- unique numbers assigned to every device that logs on to the Internet -- in a country of about 25 million people. That figure may not exactly reflect the current usage since, for example, people can use one IP address for several items, but it's still paltry by any modern measure. The United States has more than 1.5 billion IP addresses.

Still, even if most North Koreans aren't Web-savvy by design, a dangerous handful of them may be.

Jang Se-yul, who claims he worked as a computer expert for North Korea's government before defecting seven years ago, told CNN he thinks that Pyongyang has 1,800 cyberwarriors stationed around the world. He says even the agents themselves don't know how many others work for the secretive group -- called Bureau 121 -- whose mission is to "conduct cyberattacks against overseas and enemy states."

An FBI investigation linked the malware, infrastructure and techniques used by the Guardians of Peace in the Sony attack to previous North Korean cyberattacks.

After that, U.S. President Barack Obama called the hack "an act of cybervandalism that was very costly, very expensive," though he stopped sort of calling it an act of war.

The next question is: Will Kim, in Pyongyang, say the same about his country's Internet issues?

CNN's Dana Ford, Ralph Ellis, Samuel Burke, Jose Pagliery, Jethro Mullen, Hala Gorani and Catherine E. Shoichet contributed to this report.