You can prevent Hidden for iOS being uninstalled by using Restrictions. iOS Restrictions will allow you to ask for a password when trying to uninstall an app on your device.

To do this, go to the Settings app on your devices home screen, tap 'General', scroll down, tap 'Restrictions', tap 'Enable Restrictions', create a four digit passcode and enter it again when prompted, and then toggle 'Deleting Apps' to OFF.

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