NY Times:

WASHINGTON — The trail that led American officials to blame North Korea for the destructive cyberattack on Sony Pictures Entertainment in November winds back to 2010, when the National Security Agency scrambled to break into the computer systems of a country considered one of the most impenetrable targets on earth.

Spurred by growing concern about North Korea’s maturing capabilities, the American spy agency drilled into the Chinese networks that connect North Korea to the outside world, picked through connections in Malaysia favored by North Korean hackers and penetrated directly into the North with the help of South Korea and other American allies, according to former United States and foreign officials, computer experts later briefed on the operations and a newly disclosed N.S.A. document.

A classified security agency program expanded into an ambitious effort, officials said, to place malware that could track the internal workings of many of the computers and networks used by the North’s hackers, a force that South Korea’s military recently said numbers roughly 6,000 people. Most are commanded by the country’s main intelligence service, called the Reconnaissance General Bureau, and Bureau 121, its secretive hacking unit, with a large outpost in China.

The evidence gathered by the “early warning radar” of software painstakingly hidden to monitor North Korea’s activities proved critical in persuading President Obama to accuse the government of Kim Jong-un of ordering the Sony attack, according to the officials and experts, who spoke on the condition of anonymity about the classified N.S.A. operation.

[...]

Still, the sophistication of the Sony hack was such that many experts say they are skeptical that North Korea was the culprit, or the lone culprit. They have suggested it was an insider, a disgruntled Sony ex-employee or an outside group cleverly mimicking North Korean hackers. Many remain unconvinced by the efforts of the F.B.I. director, James B. Comey, to answer critics by disclosing some of the American evidence.

Mr. Comey told the same Fordham conference that the North Koreans got “sloppy” in hiding their tracks, and that hackers periodically “connected directly and we could see them.”

“And we could see that the I.P. addresses that were being used to post and to send the emails were coming from I.P.s that were exclusively used by the North Koreans,” he said. Some of those addresses appear to be in China, experts say.

The skeptics say, however, that it would not be that difficult for hackers who wanted to appear to be North Korean to fake their whereabouts. Mr. Comey said there was other evidence he could not discuss. So did Adm. Michael S. Rogers, the N.S.A. director, who told the Fordham conference that after reviewing the classified data he had “high confidence” the North had ordered the action.


FWIW.

Cheers,
Scott.