Part of me, thinks that their systems were attacked, but being into security, I've though a lot about how to attack a large computer system like this. Since server failiures are so common, the system should be able to handle N failiures before anything bad happens. If this was an attack, I guess the attacker must have found a flaw that allowed them to instantly compromise any server. But it actually seems more likely that this was caused, merely, by incompetence.

If the attack was possible, than it was just as likely, if not more, that Delta managed to merely shoot itself in the foot.