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.
Footnote originally 讛注专转 砖讜诇讬讬诐 is an Israeli film written and directed by Joseph Cedar. The film is about a very strange dramatic bureaucratic situation, where two professors, a father and a son, are in the same field, and one of them gets a honorary award for his achievements. But the bureaucrats made a mistake and told about the award to the wrong one of them.