If you’re not familiar with RUUs, they’re a ROM Update Utility application that generally runs on Windows platforms. They contain all the needed contents to take your phone from a messed up heap to a working stock blank phone again.
Yesterday RUUs for software version 2.16.65x.4 of the Sprint HTC One M8 regular and Harmon/Kardon editions were released. These enable you to take a phone, flash the most current radios, firmware, and ROM on your device and end up with it looking like it was when you first got it out of the box.
It may be worth mentioning that you do not need to be rooted to run an RUU. If your phone is borked, these are the first things a repair shop runs when attempting to get it back up and running normally. It should also be mentioned it’s going to wipe out everything and you’ll have to set it up like a new phone.
The RUU wipes the ROM, and depending on how you have things set up may clear out anything you have saved on the internal storage, so be wary of it. RUUs are generally a last-ditch effort to get a phone back into shape after something has seriously mangled the ROM, so remember you’re using a stick of dynamite when using these.
If you’re running encrypted storage, make sure to back up your photos and videos as an RUU doesn’t care about encrypted storage.
You can run either RUU on a Sprint HTC One M8. The only difference is a boot screen and some audio software that’s included. Fans of Boomsound will claim the HK mods sound terrible, and vice versa. It’s pretty subjective so just get whatever you want.[xda-developers]