I bought a THL T9 Plus recently and get some preintalled apps on it, like YouTube. I thought, that this apps are original, because Google Play client recognised these too. My phone behaved strange in some cases, so I tested it with Malwarebytes Anti-Malware.
It found: Android/Trojan.Spy.Agent.YQ in system/priv-app/thl_YouTube folder.
To remove or freeze pre-order installed apps you need to root your device - without rooting you cannot uninstall system apps (those that came bundled with the OS )
Use this guide to root
Install Titanium Backup to uninstall. There are other root apps that can do this as well but this app is highly recommended for this as also many other things it can do, which you can read in Titanium Backup
Convert you tube app into user app ( see Can I convert a system app to a user app, uninstall it, or move it to my SD card? ) followed by uninstalling it and installing from play store
Yet another alternative is to flash a custom ROM
, after due diligence
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