The terms of service for my bank's mobile banking include this:
USER MOBILE BANKING SECURITY RESPONSIBILITIES
Ensure the Mobile Device is updated with the latest system software provided by the mobile carrier or device manufacturer;
Do not modify the Mobile Device to bypass security features or replace the system software;
The app refuses to run on a rooted device. I expect them to point to that last thing about modifying the device to justify it. But does a software change legally constitute "modify[ing] the Mobile Device"? It feels to me like a modification to the device would necessarily be a hardware change.