The Russian press says the reason North Korean websites are down is due to a cyber attack.
I would take this with a grain of salt, the report comes from an "informed" anonymous source, and also that paper is a product of colder times. It is possible but comes-off as unsubstantiated fear-mongering from the Russian Press. There appears to be somewhat of a media-blackout from the West reporting this; that is surprising considering the AP has a group in Pyongyang that has been silent since the DPRK domain went down. If it were outside attackers, DPRK would be more than happy to allow the western reporters to cover this story (there are still lines of communication open).
The blackout fits within the DPRK's modus operandi as a means to escalate the menacing appearance; its a kind of wild card to play: increase the level of caution, causing hesitation among outsiders, in order to find an opening or force a move from US/ROK. This seems to fit better with tendencies of that regime. If something happens in the next 96 hrs, it will be Friday/Saturday night, in accordance with the lull in the news cycle.
DPRK is holding drills of their own, and it turns out they are running into basic problems like a lack of driver-training; fuel is severely rationed and there are not enough competent drivers to maintain the logistics of a massive war effort. In the past 48hrs, DPRK has flown over 700 sorties -burning a hell of a lot of fuel that they don't have much of.
Hacking the internet seems like a pretty dumb move from an outside perspective. That gives us less of a chance to even have our own perspective on things, something that seems important when we're dealing with such a closed country. And I can't help but wonder if the press and enthusiasts like us are hurting more over this than the NK government itself.
I'm in the camp that believes this was self-imposed by DPRK, and is little more than their hostile gamesmanship. News-junkies are certainly groping for a fix but the lack of coverage suggests that the western media is is not going to provide free DPRK fear dissemination.