It was at that moment a simple change of the password. The benefit was that people outside of our company wouldn't have access (thus not sharing it further), an

It was at that moment a simple change of the password. The benefit was that people outside of our company wouldn't have access (thus not sharing it further), and then as a future improvement we could have implemented some better key scheme. But while customers want to have root access it is not an option. Theoretically we could implement a scheme with individual passwords or keys per device (as someone suggested in the comments above), but such thing is not being prioritized by our company, so that's our fault.