Well I did this once before (had root access)
But then I realised that it can be done without root access too . That was when I asked a guy at a retail store , he told me that there is a bitten combination you press along with keys from the dailer to install the app
@EddyOS I have provided a download link in my post . Hence have linked it if someone without the one browsing through this thread would like to download it onto their device .
An update # there is a saperate package installer called demo app package installer which has the permissions to modify some parts of the filesystem without actually having root access on a device. So we could somehow use this installer to install su binary in the phone ! Helping in a one-click -root process for HTC devices
I know this thread is old but I have bought a phone from EBay (HTC One mini 2) and it had this app already installed.
I did my research and I have found out the following.
At retail stores, they can activate the app via dialing *#*#339999#*#*, then a warning pops up advising not to install it unless you are a seller with the purpose to display the phone or so....
To deactivate the app itself you need to dial *#*#336666#*#*, choose Factory Reset option and the password should be your Serial Number (S/N) of your device, which you can find in settings>about>Phone Identity.
After you do the factory reset you must have WiFi access and log in your credentials (google+, google account) as fast as possible otherwise the demo.apk installs itself and runs and the thing starts all over again.
I took me a day to suppress the demo.apk, however I did NOT MANAGE to delete it, as it turns out it installs itself on the system directory and that's why a hard reset won't wipe it.
Now basically, I have the Demo app installed on my HTC One mini 2 but as long as I don't press it nothing happens but the annoying fact is that it is still there and can not be deleted, however I have gained access on my phone.
I would advise not to install this app in any way, but if you are in my situation just follow my steps, (it took me about 4 or 5 attempts), and after you suppress the app from autorunning just hide it from the apps list, this way you won't press it accidentally again.
This should work on some other HTC models also.