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.
During the making of Close Encounters Of The Third Kind Steven Spielberg was already kind of a big man in Hollywood. But from the other side he was still young. Technically speaking this was his third theatrical film. He did work for television from the late 60s. At that time he already directed a number of feature length TV movies. One of them was the famous Duel. And then he did only 2 theatrical pictures: the 1972's The Sugarland Express and the 1974's Jaws. And now there is this movie.