North Korea may have had help from the hackers who hit Sony in 2011

“These gamers had been trolling Sony for years,” Clements says. “They had compromised credentials; who knows who they shared that with in the underground?”

In past breaches, Sony had come under fire from multiple groups at the same time. Sony was warned in late-2013 that hackers were stealing gigabytes of data from its network several times a week, underscoring a pattern of security lapses that predated the recent attack, Bloomberg News reported. At least three hacking groups had infiltrated the PlayStation Network at the time of the 2011 hack. The one that did the most damage was a Russian cyber-crime ring that had been inside of the network for at least two years, stealing and reselling video games.

Tracking hackers is tough. Because of advances in hacking capabilities, it’s often difficult to tell the difference between state-sponsored attackers and independent groups, says Bruce Schneier, a prominent cyber-security author, blogger and chief technology officer at Co3 Systems. He says he’s “deeply skeptical” that North Korea is behind the Sony attack. “Hackers have loved to hate Sony for a decade,” Schneier says.