A bootloader is a vendor-proprietary image that is responsible for bringing up the kernel on an Android device. It is the first program that runs when the phone is powered on and is responsible for initializing the Trusted Execution Environment (TEE) and binding its root of trust. The bootloader also verifies the integrity of the boot and recovery partitions before moving execution to the kernel. By default, most Android devices ship with a locked bootloader, meaning that users cant flash the bootloader or device partitions. Unlocking the bootloader allows users to install custom firmware on their Android phone and gives them full access privileges to make modifications to the phone. Some developers and enthusiasts unlock and root their devices to experiment with applications or custom builds of Android. Locking the bootloader is important for data security, as it prevents ROM/firmware from unwanted modifications and plays an important role in data security, protecting personal data against theft.