Can you keep a secret? Yes, you could secretly control someone's props… but it would be hard/unlikely.
In order for the app to control a prop/group, the group must be placed into the setting page (page 5 mode 1) while the app is trying to connect to it. So if you were a determined and patient prankster, AND your quarry happened to go to their setting page, AND stay in mode 1 long enough without entering adjust… you could possibly secretly connect to their props… but could you keep that secret? ;)