Hello Ruben,
Taking into consideration your requirements I would recommend running this task on LocalSystem account. If you decide to do so, just go to "Scheduled tasks" page, double click on the task and go to "Account" tab. Leave the "User" field empty.
However, as a workaround you could configure the scheduled task to run on LocalSystem Account. In this way the task will run at every user logon but on LocalSystem account. Please note that if you configure a task to run under LocalSystem, the GUI of the application launched by the task will be hidden.
Another method would be to avoid using our "Scheduled Tasks" feature and to add a shortcut of the file launched by the scheduled task in the alluser start-up folder: C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
Please take a look here :
How to launch application at logon/startup
Best regards,
Sorin