If it really does become apparent that terrorists are using GPS to guide their unmanned bombs (I highly doubt that and think the hijacking of a plane still is the easiest way to achieve the bad guys ends), then I am of the understanding that an error can be intentionally introduced into the GPS network. Now even if 1 Nautical Mile was introduced into the network and we had to run 7NM between all ADSB traffic it still beats 30NM RNAV standards that we run currently in non radar airspace.
AirNoServicesAustralia, to introduce a large error to the civy GPS signal would cause huge problems - which is what worrys me
IMHO, with the ADS-B system, we are going to get too reliant on a fragile GPS based air-nav system.