Going back to what the threat to aviation security would be. So the logic would be that a person trying to cause harm to an aircraft would:

1. Board a flight, and place the salt in a location of the aircraft somewhere critical that is also aluminum.
2. Note the tail number of the aircraft.
3. Hope maintenance misses it for many months.
4. Keep reading the news looking for stories of downed aircraft and compare the tail number from step two.

Seems a little far fetched to me.