The White House called the cyber-attack on Sony Pictures a serious national security matter Thursday, threatening an "appropriate response" as others pointed the finger at Pyongyang.

With the Hollywood scandal threatening to escalate into geopolitical crisis, Sony defended its decision to cancel the release of "The Interview," a movie about a fictional CIA plot to kill Kim Jong-Un.

"This is bigger than us," the studio insisted, as footage that leaked onto the Internet showed that the film's climax was to have been a graphic close-up of the North Korean leader's fiery death.

White House spokesman Josh Earnest declined to confirm reports that North Korea had attacked the movie giant, which pulled the film after hackers invoked September 11, 2001 in threatening attacks on cinemas.

But, in a sign US intelligence believes the attack came from an enemy of the United States, he said: "The president considers this to be a serious national security matter."

Earnest said the attack, which saw hackers gain access to a trove of internal Sony documents, was carried out by a "sophisticated actor."

"There has been destructive activity with malicious intent, and the administration believes that that activity merits an appropriate response from the United States," he told reporters.

- US options unclear -

Others have been less reluctant to point the finger. A Sony source told AFP that, while it was up to US authorities to determine what happened, the studio believes Pyongyang was behind it.

"We don't know, but it appears so," said the source.

It's unclear what measures the United States could take if it determines Pyongyang was behind the cyber attack against Sony.

Experts argue North Korea could be testing the US and probing where it is vulnerable in cyberspace, and as such a strong response is needed.

"A weak response will only embolden North Korea and lead to more serious attacks, even if it is not proven to be the culprit," wrote Bruce Bennett, senior defense analyst with the RAND Corporation.

North Korea has denied involvement in the brazen November 24 cyber attack, which experts say could have been carried out by disgruntled Sony workers or by supporters of a foreign power.

Sony cancelled the film's December 25 release after major US theater chains said they would not screen "The Interview," a mad-cap comedy in which two television journalists are recruited to assassinate Kim.

Free speech advocates and foreign policy hawks slammed the decision as cowardice in the face of a hidden enemy.

Former presidential nominee Senator John McCain lashed Sony for backing down, a few days after the so-called Guardians of Peace hacker group threatened cinema-goers.

"By effectively yielding to aggressive acts of cyber-terrorism by North Korea, that decision sets a troubling precedent that will only empower and embolden bad actors to use cyber as an offensive weapon even more aggressively in the future," said McCain.

A Sony source said the Hollywood studio had no choice.

"This was a terrorist act, and you don't take that lightly," the source said, adding: "This is much bigger than us ... it's a whole new world, now warfare is on the cyber level."

- 'Very dangerous precedent' -

Experts said Sony's decision sets a dangerous precedent.

"I am sympathetic with Sony and I am sympathetic with any theater that worries about damage and injury and worse involving its staff and its customers," said Richard Walter of the UCLA Film School.

"But on the other hand I have to say there is something, for an American and for anybody who loves freedom, that viscerally rebels against surrendering to terror this way," he told AFP.

Former House Speaker Newt Gingrich said this week's events should sound alarm bells. "With the Sony collapse America has lost its first cyberwar. This is a very very dangerous precedent," he said on Twitter.

In addition to threats, Sony has seen the release of a trove of embarrassing emails, scripts and other internal communications, including information about salaries and employee health records.

"The Interview" is not the only film suffering because of North Korea's ire: a planned Steve Carell movie, "Pyongyang," about a Westerner's experiences of living in the hermit state, has been scrapped, according to industry media.

On Thursday, reports suggested that Paramount had nixed some theaters' plans to screen "Team America: World Police" -- a 2004 puppet-driven parody with former North Korean leader Kim Jong-Il portrayed as the villain -- in place of the comedy film cancelled this week.

Also Thursday, Brazilian author Paulo Coelho offered to pay Sony $100,000 for rights to "The Interview," saying on Twitter that he would then post it free on his blog.

Separately, the UN General Assembly called for North Korea to be referred to the International Criminal Court over its dismal rights record, in a landmark resolution adopted by a strong majority.

Hackers may have exploited Sony's weakest link: humans
San Francisco (AFP) Dec 19, 2014 - Hackers who forced Sony Pictures to abort release of a comedy about North Korea likely slipped past the entertainment titan's defenses by exploiting a weak spot -- humans.

That suspicion prevailed on Thursday among cyber security specialists piecing together clues about an attack that led Sony to cancel the release of "The Interview," a movie about a fictional CIA plot to kill North Korean dictator Kim Jong-Un.

The attack, branded by White House officials as "a serious national security matter," was seen as vindictive or even personal, with hackers out to cause Sony extreme pain instead of being driven by the typical profit motive.

Sony workers may have been targeted with "spearphishing" attacks that sent specific workers bogus email messages that appeared to come from trustable sources, according to Usher online identity platform senior vice president Guy Levy-Yurista.

Such deceptive missives typically include web links or attached files which, if opened, result in computers being secretly infected with malicious software.

"The weakest link in any security system is always the human being," Levy-Yurista told AFP.

"My guess is that North Korea made a decision to go after Sony; started a quick spearphishing campaign aimed at Sony Pictures or other parts of the company and then gained access to the system."

Once hackers get footholds, they take advantage of security holes to seize control and data.

The malicious code that infected Sony Pictures was identified as a customized version of Destover. A similar hacker tool has been used in cyber attacks on banks in South Korea and corporations in the Middle East, including Saudi Aramco.

The virus spreads quickly, sucks up data and then destroys computer hard drives to cover its tracks.

"It literally shreds the hard drives of all those machines so they are useless," said Levy-Yurista.

"It is quite impressive what they have done. It is also quite horrific."

- Out to hurt Sony -

CloudFlare principle security researcher Marc Rogers, who is chief of security at the notorious annual Def Con hacker gathering in Las Vegas, is studying leaked Sony files for insights into the attack.

Rogers found that once past the perimeter of Sony's computer system, data was scantly protected with "egregious" flaws such as unencrypted files and passwords stored in plain text.

Hackers could have pillaged financial accounts or even tried extortion, he reasoned.

"It seems clear that whoever was behind this wasn't after money, they were out to hurt Sony," Rogers told AFP.

"It feels more like an insider job to me."

A disgruntled employee could have opened a path for hackers, and then lax security inside the system let them run amok in the network, according to Rogers.

In addition to receiving threats, Sony has seen the release of a trove of embarrassing emails, scripts and other internal communications, including information about salaries and employee health records.

The mountain of stolen data indicated attackers were inside Sony's network undetected for a while, or even had physical access to machines.

Whoever attacked Sony could have used off-the-shelf hacker tools, and appeared to be savvy in ways of distributing stolen data online.

Spearphishing is a standard tactic used for targeted cyber attacks, although it remained unclear whether the ruse was used on Sony Pictures, according to Symantec security response team director Kevin Haley.

"I can pick out a name, do some social engineering in the email, entice them to an attachment or link, and it goes to malware," Haley said.

Hackers are also known to use a watering hole attack in which a website popular in an industry is broken into and rigged with code that pounces when prey visits, according to Haley.

"The idea is that the lion doesn't have to search around the jungle looking for food; it just sits at the water hole and waits," Haley said.

- Film climax leaked -

Sony defended its decision to cancel the release as footage leaked onto the Internet showing the film's climax was to have been a graphic close-up of the North Korean leader's fiery death.

White House spokesman Josh Earnest declined to confirm reports that North Korea had attacked the movie giant, which pulled the film after hackers invoked 9/11 in threatening attacks on cinemas.

But, in a sign US intelligence believes that the attack came from an enemy of the United States, he said: "The president considers this to be a serious national security matter."

North Korea has denied involvement in the brazen November 24 cyber attack.