Factory reset or wipe is often used not just to start fresh but to also as a necessary step when selling a used Android device. Well, that's the theory anyway. Researchers from Cambridge University claim that they are just that: theories. Unfortunately, in practice, that might not be completely the case. Their tinkering of 21 smartphones from five manufacturers, all running Android versions 2.3 t 4.3, showed that factory wipe actually leaves some data locations intact. Worse, some of these locations are the very places that store credentials and encryptions keys that are supposed to be private and safeguarded.