wtf do you mean "what happened" where the fuck have you been?
They believe Anonymous did it, they're politically correct and do things just to prove a point. Point being, lul ps3 security sux. they just ping the server repeatedly with whatever program they use crash the server Since PS3 has no idea what the hacker actually did, like if the Hacker actually took credit card information they just assume it was Anon. (Rightfully so, Anon has claimed for a while that PS3's security is a joke and made it public that they could if they wanted to) plus this happened the week Portal 2 was released and the Ps3 version of the game had Valve online (Counterstrike,halflife) so the PS3 version of the game had better online content.
Summary: Hackers pinged servers until it crashed, gained access put breadcrumbs everywhere just to let PS3 know they were there. PS3 has no idea WTF happened, warns everybody to put their bank accounts on high alert. Feel pretty stupid right about now for having lackluster security