With Android 6.0 Marshmallow, Google started warning users that the system integrity of their device is compromised if the system partitions of the device were touched in any way. With Android 7.0 Nougat, Google says that a device whose system integrity is compromised will stop booting completely.
In a nutshell, this means that if a malware has infected your Android device and is sitting silently inside the system partition, your Android device will not boot into the OS at all. This way, the malware will not be able to steal your personal data or cause any harm. To avoid the inconvenience of your smartphone suddenly not working, Google will be offering a limited Direct Boot feature in Nougat. Under this mode, the system boots with a limited number of apps and features working.
If you are someone who uses Xposed framework or roots their device, don’t worry. Google says that this security check is only enforced on devices with a locked bootloader, and it automatically stops the check on devices whose bootloaders are unlocked. This way, you can flash custom ROMs or root your device without worrying that it will stop booting altogether.
This feature will only be available on devices that run Android 7.0 Nougat out of the box, so owners of existing Nexus and other high-end flagship Android devices are out of luck here.
[Via Android Developers]