How do I fix [Authentication Fail #9] [Modified]?

telorast

    OK, I confess. I've rooted my phones for years. Today I decided to remove some apps that I thought were unnecessary on my LG K7 & went apparently went one too far. When I rebooted, I got:

    Security error

    [Authentication Fail #9] [Modified]

    The phone has been rooted for as long as I've had it (close to a year) with no problems. I haven't done anything else like unlocking the bootloader or adding a custom rom... just the basic root. The problem may or may not have been caused by uninstalling the Easy Home app.

     

    Of course there are any number of suggestions online for fixing the phone. The one that seemed reasonable was to use the LG support tool on my PC. It seems best to ask here about the steps involved or to find out if I should fix things some other way. I could take it to the T-Mobile store but I like to fix things myself when there's a way. It's OK if you want to lecture me... 

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