According to VentureBeat, "Sony shut down its Playstation Network after a new custom firmware version for the console let users download games and content with a fake credit card number, according to a moderator from Playstation fan-site PSX-Scene."
The actual quote from the moderator is taken out of context. It mentions the latest release of, "CFW (custom firmware) released known as Rebug (http://rebug.me). It essentially turns a retail console into a dev console (not fully, but gives you a lot of the same options that usually dev's only have access to)..."
However, the poster then states:
"dit #3: Ok, it looks like some various news sites have picked up this story and taken it out of context. Once again, this is all speculation and information gathered from various devs in the PS3 scene. It might very well not be the real reason PSN is down, but as the timeline fits, it's a reasonable explanation.
"Now, as to Rebug directly allowing this to happen, that's not the case at all. Different CFW's have had access to the dev network the whole time. This is not new news for people in the PS3 scene. It's what people have figured out what to do with the said network that has caused all the recent issues. Saying that Rebug is what did this is like saying a gun manufacturer is responsible for every death that happens with a gun."
So, calm down on that "Credit Card Hack!!" mongering.