Maybe Sony hasn't confirmed all the reasons why the PlayStation Network is down.
We've known for some time that, officially, it was due to an "external intrusion," but something else has come to light: according to PSX-Scene moderator chesh420, Sony shut down the PSN due to a custom firmware called Rebug . Basically, this allowed users to simulate a PS3 debug unit (something we and other sources have to play betas and certain games early); with a few proxy-server changes, Rebug lets a retail PS3 mimic a debug PS3. So, when the hacker inputs false credit card numbers, Sony doesn't check them because they assume developers or journalists are logged in. So yeah, they can then get the PSN stuff for free and that's a definite problem. Of course, all of this is speculation – as admitted by chesh420 – and Sony hasn't said anything about Rebug being the cause of the PSN downtime.
Whatever the reason, it'll be interesting to hear Sony's detailed explanation on the entire issue…provided they ever provide one.