Where does occam's blade of decision fall:
1) Attention starved country paid for hack and then released embarrassing info from a Japanese _associated_ company. Japan and Best Korea don't get along well. I'm aware Sony pictures is a USA company, but Sony is a well known international brand for Japan.
2) Provocative movie producers engineer (how?) a hack to embarrass their movie distributor (why?) and bring attention to movie that was already provocative enough and over exposed enough.
3) Ex-employees of Sony who were laid off recently decide to drop a digital e-turd in Sony's punch bowl and were happy enough when the blame was placed on #1 above.
I'm voting for #3, and possibly #2 as a kind of performance art piece, but #1 just doesn't sound plausible.