They claim it's a weather satellite. It seems to have a polar orbit, probably sun-synchronous. Basically, three kinds of satellites use that sort of orbit; meteorological, mapping, and spy satellites. The former in order to monitor things like global temperature and improve weather forecast modeling, the latter two because it keeps the shadow angles the same on each pass and provides global coverage. I seriously doubt the north koreans put a satellite up there to check for global warming or see if polar bears are stranded on ice floats. The old Keyhole spy satellites (aka Big Bird) also used these kinds of orbits. It makes sense that they would start off using that kind of orbit for a spy satellite themselves - a polar orbit grants global coverage.