If someone breaks into your locked house, but the locks are made of string and the doors made of paper, and the same computer is stolen then you'd be outraged but I doubt anyone would have sympathy for you. It could be reasonably said to be your fault. Sure, the thief should never have been there, but acting like he doesn't exist or hoping that he won't find your house are not defensible stances in the real world.
Locks and security only stop honest people (or people very poor at being dishonest).
If you put up a sign saying do not steal, and no other security, whose fault is it if the item behind the sign is stolen? The theif (feel free to disagree), for had
they not taken it, it would still be there.
If you put up a sign saying danger minefield, and no other security, whose fault is it if someone (who saw the sign and can read) steps a mine? The victim (feel free to disagree). Well it cant be the victim, they read the sign.
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Sure, sony should take resonable and responsible precautions, but ultimately, to stop an honest person, they would have made the data inaccessable by accident, but beyond that, to try to keep up with, in this case, hackers, really what is the point in trying. If you get hacked by someone who is not a accidental visitor, whos fault is it, theirs, all theirs.