My biggest concern here is that Sony is investigating it...meaning they knew of nothing happening.
This can mean various things:
1. These hackers only said that they hacked Sony, because Sony so far knows nothing about the attacks apart from a few tweets. I am only speculating here, but it could be the case.
2. Sony's network security manager is not doing his job (still just speculating). I work in IT and I know that scaling a massive database puts strain on a network. If no one notices that much activity going on (especially right after a massive attack that shut down its online gaming platform), something is wrong there. This could also mean that the attack never actually took place.
That was all pure speculation. What I do know is that these hackers might be really good with doing this, but they don't think their plans through. Hack Sony and then what? Sony won't shut down, they make tons of money from other aspects that are completely unrelated to gaming. TONS. The only people that really suffer here are users of PSN...they were unable to play online for like a month and their personal data was scaled. Basically, these assholes are actually just attacking PSN users.