Attribution Is Difficult If Not Impossible
First off, we have to say that attribution in breaches is difficult. Assertions about who is behind any attack should be treated with a hefty dose of skepticism. Skilled hackers use proxy machines and false IP addresses to cover their tracks or plant false clues inside their malware to throw investigators off their trail. When hackers are identified and apprehended, it’s generally because they’ve made mistakes or because a cohort got arrested and turned informant.
Nation-state attacks often can be distinguished by their level of sophistication and modus operandi, but attribution is no less difficult. It’s easy for attackers to plant false flags that point to North Korea or another nation as the culprit.
A list of previous Sony Hacks here.