Federal Web sites knocked out by cyber attack
sfgate.com
sfgate.com
However, North Korea has a pattern of showing force to generate internal support for its government and as a playing card in negotiations with the west. Cyber-attacks like these are not flashy like testing a missile or a nuclear war-head and not very good for propaganda machine.
And keep in mind this is a DoS attack against public-facing websites. Taking a SK newspaper site offline is really annoying but it's not exactly in the same league as hacking the electrical grid.