US NSA hacked DPRK years before Sony attack

It's the first time the United States has publicly charged another government with mounting a cyberattack on American targets.

But the New York Times also raised questions about why the United States was not able to alert Sony beforehand about the attack, which the US said was probably caused by the release of "The Interview," a movie that features an assassination attempt against DPRK leader Kim Jong Un.

Pyongyang has repeatedly denied any involvement in the Sony hack.

Many experts are skeptical that DPRK was the culprit, or the lone culprit, suggesting that it was an insider, a disgruntled Sony ex-employee or an outside group mimicking DPRK hackers, the newspaper said.

"Many remain unconvinced," said the report. "It would not be that difficult for hackers who wanted to appear to be North Korean to fake their whereabouts."