I've moved on from a previous job, and as part of the process I need to return my work provided phone.
I have factory reset the phone, as well as electing to erase the SD card. There was some sensitive data on the phone (pictures, documents etc) that I want to make sure are unavailable to whoever uses the phone next.
Can I be certain that this data cannot be recovered via an undelete application? Does the factory reset + erase sd write zeros to the drives or simply mark them as empty space?