Back Door is a form of malicious feature in which the program is configured to respond to commands sent to it from the developer. A Universal Back Door is an ability of the developer to remotely change the program to do anything the developer desires it to do. Sometimes Universal Back Doors are called "Auto-Update".
This comment thread is for people to document various implementations of this malicious feature.
A lot of electrical devices today have a switch of some kind to deactivate the device after a certain period of time. Sometimes the device just gets annoyingly slow. In any case, it is implemented in software on that device. And the reason for that is Planned Obsolescence. Forcing the user to throw away this device and buy a new one.