The CIA has been known to tamper with electronics, so between that and pre-backdoored hardware (IME) it's fairly likely that a determined opponent has one or mo

The CIA has been known to tamper with electronics, so between that and pre-backdoored hardware (IME) it's fairly likely that a determined opponent has one or more means to passively wait for a payload in a hard to detect manner. From there, it's turtles all the way down; you "only" need to deliver an ulterior, possibly tailored, payload from any of the several methods described in this thread.