This may be old news but thought I'd pass it along anyways. There is an article in the June 2006 issue of Avionics talking about the need for secure ACARS. It specifically mentions hobbyists trying to track flights. Sounds like there is a strong move from the airlines industry to develop a standard that will be defined as ARINC 823. The article also mentions that there is a parallel push by the Air Force for the same.
http://www.avionicsmagazine.com/cgi/av/show_mag.cgi?pub=av&mon=0606&file=securingacars.htm
Regards
Dan
Apple Valley, MN
http://www.avionicsmagazine.com/cgi/av/show_mag.cgi?pub=av&mon=0606&file=securingacars.htm
Regards
Dan
Apple Valley, MN