North Korea is most likely not responsible for the cyberattacks against Sony Pictures Entertainment, which saw thousands of sensitive internal documents released on the Web in a high-profile strike, experts said.
The secretive nation has been fingered in part because the same malware was used against Sony that crippled South Korea in March 2013. Those attacks, dubbed "Dark Seoul," wiped data from banks' computers, disabled ATMs and crippled websites.
It was also theorized that North Korea was angry about a forthcoming movie in the U.S., "The Interview," a comedy in which two show business reporters travel to North Korea to interview leader Kim Jong Un.
But the Sony attacks have been a more public affair, with taunting images displayed on hacked PCs, sensitive company documents posted online and gigabytes of leaked documents sent to journalists.
They are not tactics normally associated with state-sponsored attacks, said Lucas Zaichkowsky, an enterprise defense architect with Resolution1 Security.
"That is almost certainly a hacktivist play," said Zaichkowsky in a phone interview Wednesday.
Zaichkowsky used for work for Mandiant, the computer forensics company now owned by FireEye that has been reportedly contracted by Sony to investigate the attacks. He said the release of gigabytes of data seems more like a move that would come from hacktivists, possibly with connections to disgruntled employees.
A hacking group calling itself the Guardians of Peace (GOP) has claimed responsibility, and a self-proclaimed leader of the group has been sending data to reporters, including IDG News Service.
The group said in an email it was not working on behalf of any state and said its actions against Sony were in part related to the company's restructuring efforts and labor issues.
"Sony and Sony Pictures have made terrible racial discrimination and human rights violation, indiscriminate tyranny and restructuring in recent years," GOP wrote. "It has brought damage to a lot of people, some of whom are among us."
The group said corporate restructuring was the "decisive motive of our action" and called on Sony to "stop this and pay proper monetary compensation to the victims."
"We have another plan to correct the incidents of Michael Brown," the email to reporters added, referring to the fatal shooting of an unarmed man by a police officer in Ferguson, Missouri.
These are hardly the normal concerns of North Korea, and the message doesn't mention "The Interview" at all. It's more consistent with attacks by activist hackers due to its attention-seeking nature, public posting of links to stolen files on Pastebin and reference to social causes.
Jamie Blasco, director of AlienVault Labs, has been analyzing the malware and said the attackers seem to have had knowledge of Sony's internal network.
"The malware samples contain hardcoded names of servers inside Sony's network and even credentials/usernames and passwords that the malware uses to connect to systems inside the network," he said.
Former Sony employees might have that kind of network knowledge, but hackers also often do reconnaissance on networks prior to an attack, looking for weak points to exploit.
Although attributing cyberattacks is difficult, it's unlikely North Korea is behind Sony's troubles, said Scot. A. Terban, a threat intelligence analyst who writes under the Twitter handle @krypt3ia.
The style of malware used against Sony, which corrupts a computer's master boot record, has been around for 16 years, Terban said in a phone interview Wednesday.
It is possible that the Sony attackers obtained the same malware that was used against South Korea last year, as the malware is available on the internet. The attackers may have changed it a bit to avoid security software and then repurposed it, he said.
Terban said the use of Korean language encoding in the malware is still "not a lot to hang your hat on as far as attribution goes."
If North Korea had indeed struck Sony, "there would be no evidence of Korean coding" in the malware, Terban said.
Read more: Sony Hack Attack
McAfee, a computer security company now owned by Intel, did extensive research into the Dark Seoul attacks, publishing a technical report on the malware in July 2013.
Its analysts wrote the March 2013 attacks were actually the conclusion of a four-year covert espionage campaign that also sought classified military data.
Two groups, called the Whois Hacking Team and the NewRomanic Cyber Army Team, conducted the Dark Seoul attacks, but McAfee concluded they were likely part of the same team since they used similar attack code.
McAfee declined an interview request Thursday asking if its researchers were still tracking the groups.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com