"You can't prove that they don't already do X, because X is by definition a secret action" is a pretty useless epistemology though. Every electronic device you've ever used could secretly have a cellular modem that can secretly download over-the-air firmware updates that alter its behavior to be maximally evil. You by definition can't prove that your coffee machine doesn't secretly have the ability to change its behavior to start connecting to the internet and DDOSing charities or something.