The message Sony Pictures employees saw when they got to work Nov. 24
A security company in the U.S. has provided further evidence that last year's devastating hacking attack on Sony Pictures Entertainment was carried out by a group with ties to North Korea.
The FBI has already named North Korea as the source of the attack, but some security experts have been skeptical, in part because the FBI didn't disclose all the details of its investigation.
Security firm CrowdStrike is among those who believe North Korea was the culprit, and on Tuesday it presented another piece of evidence to support that claim.
CrowdStrike said it found similarities between the malware used against Sony and a piece of destructive code deployed in 2013 by a group it calls Silent Chollima, which has already been linked to several attacks on South Korea and the U.S.
Parts of the code used in each attack are almost identical in their structure and functionality, CrowdStrike CTO Dmitri Alperovitch said during a webcast Tuesday in which he described how the Sony attack was carried out. (A replay will be available here.)
What's more, he said, the malware used in both attacks contains the same typographical error in the same place, spelling "security" as "secruity."
CrowdStrike had already identified similarities between attacks by Silent Chollima and the one on Sony, including the use of destructive "wiper" malware and the way that code was deployed. But it hadn't described the similarities in the code itself.
The similarities are in a part of the malware that's used to spread the code through a network. The part that does the data-wiping is considerably more advanced in the malware used against Sony, Alperovitch said, suggesting it was a later version of the same program.
Malware sometimes get shared and reused in underground forums, but the source code for the 2013 attack and the Sony attack haven't been released publicly, Alperovitch said. So it's unlikely another group of hackers could have reverse-engineered the Secret Chollima code and reproduced it exactly, right down to the typo.
"Once you go through so many 'ifs' and 'buts,' it makes it highly implausible," he said.
The group that claimed responsibility for attacking Sony calls itself Guardians of Peace. Silent Chollima often uses different names during different attacks and may have done the same with Sony.
Other security companies, including Symantec, also have linked the Sony attack to North Korea.
"We're just providing more details and additional evidence to tighten up the case," Alperovitch said.
"There's been a lot of questions about the attribution for this case, and more public evidence will help people make up their own minds about who's really responsible," he said.
In December, the FBI publicly blamed North Korea for the attack, which led to reams of company data being published on the Web, including executives' emails and salary data, as well as unreleased movies.
James Niccolai covers data centers and general technology news for IDG News Service. Follow James on Twitter at @jniccolai. James's e-mail address is james_niccolai@idg.com