Disclaimer alert - the following is pure speculation, but I have a tiny bit of experience with avionics from a past job. 1) background reading: http://members

Disclaimer alert - the following is pure speculation, but I have a tiny bit of experience with avionics from a past job. 1) background reading: http://members.optusnet.com.au/~cjr/CPDLC.htm http://members.optusnet.com.au/~cjr/CPDLC.htm http://www.icao.int/APAC/Documents/edocs/GOLD_1st_Edition.pdf http://www.icao.int/APAC/Documents/edocs/GOLD_1st_Edition.pd... RTCA DO-219, if anyone can find it. 2) The slides don't provide enough details, I haven't had time to listen to the talk to see if it fills in more info - the critical part is how/if he's managed to convince the FMS to accept ACARS uplinks other than the 'harmless' three defined uplink messages that are automatically accepted by the FMS without pilot acknowledgement. My guess is that by having access to a FMS code/simulator, he figured out a buffer overflow or other hack that lets him inject FMS command messages without pilot acknowledgment, which is normally required of all other uplink messages. 3) In my admittedly tiny amount of experience, the designers of avionics communications protocols aren't dumb. They tend to be very old-school looking formats (low level, fixed fields, etc) because they were often designed when avionics equipment had little processing power, but at the same time this means that the format spec has a small surface area. Also sometimes it's possible that there's not 'security' as we think of it in terms of encrypted links, but there is often a lot of thought put into the messaging sequence (send/ack/etc), including pilot confirmation, to ensure that garbage isn't accepted.