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Some users report that this app is also installed some other apps without the owners permission, and it is impossible to remove it even with factory/hard reset. The reason for that is that this app manages to isolate its files from the main OS, and that regardless of deletion/uninstall always finds a way to reinstall itself. There are few reports of successful removal with some tools, but xHelper adjusts very quickly and disables all possible security programs.
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This might be the answer to the case that I experienced a few weeks ago. I am not sure/know whether my smartphone is infected
xHelper, but what happened to my smartphone is exactly what you mentioned.