EDIT: Planes are absorbing a tremendous amount of input from their environment at all times, both digital and analog. That input is, in many cases, being processed by software. Just to articulate the model a little further.
Keep in mind that military aircraft have tons of specialized systems on them that civillian aircraft do not. And further, that countries would be willing to spend, literally, billions of dollars to build systems that could exploit flaws like this. So even for quite exotic ideas like say, designing ground objects with exotic shapes that have radar signatures that trigger flaws in onboard processing software, or whatever.
I'm just making things up here, but there are undoubtedly teams of physicists, avionics experts and cybersecurity experts tasked with studying this, even if just to ensure our systems are not vulnerable to it. It's possible that all that has come to nothing, but it would not surprise me if it hasn't.