Verified boot was introduced to Android way back in 4.4 KitKat. It was a concern to the Android modding community back then, but we haven't really seen this surface. Google is taking this feature a bit more seriously in Android 6.0 Marshmallow. Verified boot exists to detect persistent rootkits that could stick around longer than they should compromising your devices security. If you root or bootloader unlock either the Nexus 5X or the Nexus 6p you will need to endure a 10 second boot screen warning you that your device software can't be verified for corruption, asking you to lock your bootloader. There is an included link which will take you to the nexus support page which give the below list. Yellow warning: This message lets you know that your device has a different operating system than the one that originally came on your device. Orange warning: Your device is in an “unlocked” state. This means that your operating system can’t be checked to make sure that it’s safe to use. Red warning: The operating system on your device has been changed or corrupted and is not safe to use. The device may not work properly and could expose your data to corruption and security risks. I am sure there will be ways of getting rid of this, but it is pretty annoying that it shows up at all. I guess if you used some sort of malicious root tool to root your phone it would be nice to know if it was still secretly running in the background, but not if you have just unlocked your bootloader.