Simply, yes! When you put your device in DFU Mode, it erases everything and: Deletes the passcode Removes the Apple ID and Password Put Activation Lock on your iPhone After going through the DFU, you will have to again set up your device as brand new and reenter the device's older passcode, Apple ID, and Password to disable the iCloud Lock after restoring your phone. So, if your iPhone is stolen and the thief still needs a device passcode, Apple ID, and Password to disable the iCloud lock. If he resets the iDevice via DFU Mode, (which can be used to reset the passcode), he still won’t be able to reactivate the device without removing the Activation Lock.