Confinement problem
The confinement problem is the question of how to stop a program from passing on private data it has been given. Butler Lampson posed it in 1973, picturing a customer handing private data to a service it doesn't trust. A leak doesn't need a file: it can travel through the bill, or through the load the program puts on the machine. Confinement is about what a program knows and containment is about what it can touch, so a system can be well contained and still poorly confined.
