Entities in Country A provide entities in Country B with software for, say, self-driving cars. Such cars become sufficently popular in Country B. ("Sufficiently" being read as numerous enough for the next step to become important.)

Country A and Country B come into conflict. Potential causes: resources (oil, fresh water, rare earths, whatever), ideology, etc.

Country A uses its legal (and extra-legal) powers to force the entities providing said software to push out an over-the-air update of the software. When Country A flips a switch, the self-driving cars begin moving offensively, attempting to kill passengers and pedestrians and jam the road infrastructure, doing as much economic and political damage as possible. (Whoo; suppose they target specific people and infrastructure.)

It's an entertaining scenario for your favorite TV series or something, but possibly more troubling for software controlling information networks or the power grid. And the proof-of-concept of such an attack has already been shown to be successful.

P.S. We are both assuming that self-driving cars are better than human-driven cars, which fact is not currently in evidence.