It is called selective availability. http://en.wikipedia.org/wiki/Selective_availability#Selective_availability My undergraduate thesis involved how to couple intertial senors using a Kalman filter to compensate for SA in GPS signals. Two years after my project concluded, the US disabled SA in GPS. I doubt that this recent "outage" was related to similar SA in GLONASS. Rather, perhaps it was indeed an encrypted transmission, or was based on a second independent synchronization signal only available to military assets used to put the scrambled transmissions back in the right order.