I have an HTC One bought unlocked (i.e. no simcard) with Android. I swear on my grandma's tomb that I've never tried to tamper it (I don't even know what that exactly is, I thought that made only in very closed phones such as iPhone). It was updated to the last version until a couple of days ago I got a notification to install the last update. After downloading and clicking in install it reboots the phone and I come to a bootloader which says
tampered locked security warning
some other data and gives me usual options for reset. I have read online that this happens when one 'tampers' the phone, which I haven't. There are solutions to 'untamper' it online, but I am afraid that attempting any of those solutions
As a side note: the phone was bought from HTC's US website less than a year ago, so it must still have the warranty running but I am not sure if I should contact them (I fear they say the warranty is invalid if the phone says tampered).
I believe all the apps were installed from the Google App Store. I installed F-Droid because a friend recommended it, but I never used it.
Any idea on how to get rid of this silly message, keep my phone under warranty and install the update?