The PlayStation Network will be under going maintenance tomorrow from 9:15AM PST / 12:15PM EST until 3:15PM PST / 6:15PM EST, which means that the PlayStation Store, PlayStation Home (Does anyone still use this?) and Account Management will also be offline until the maintenance is completed. To ensure that you’ll still be able to play online and have access to apps that require access to PSN you may want to sign in now or prior to the upcoming maintenance, otherwise you’ll have to wait until the maintenance has completed.
No, Sony’s PSN hasn’t been hacked again, it’s just general maintenance.
Source – PlayStation Official Forums