Update 30 June 2012: BAE has announced the development of a new navigation system, navigation via signals of opportunity (NAVSOP) radio positioning to supplement existing GPS and mitigate potential spoofing efforts (Holloway, 2012). NAVSOP will rely on existing radio infrastructure and be usable in locations where GPS currently cannot (i.e., polar Earth positions and inside buildings; Holloway, 2012).
Update 6 July 2012:This experiment is the first proof that UAS can be spoofed to change their position using automated reaction (Franceschi-Bicchierai, 2012).
Holloway, J. (2012, June). BAE takes on GPS with NAVSOP radio positioning system. Gizmag.com. Retrieved from http://www.gizmag.com/bae-navsop-radio-positioning/23137/
Franceschi-Bicchierai, L. (2012, July). Drone hijacking? That's just the start of GPS troubles. Popular Science. Retrieved from http://www.wired.com/dangerroom/2012/07/drone-hijacking/
Lecher, C. (2012, June). Texas students hijack a U.S. Government drone in midair. Popular Science. Retrieved from http://www.popsci.com/technology/article/2012-06/researchers-hack-government-drone-1000-parts
Rawnsley, A. (2011, December). Iran's alleged drone hack: Tough, but possible. Wired. Retrieved from http://www.wired.com/dangerroom/2011/12/iran-drone-hack-gps/