content: The trojan could easily attach itself to other running processes,making itself invisible and use the security access of that process. You the average user wouldnt know. This assumes a well known method. The trojan could also do firmware modifcation of BIOS/UEFI or even the firmware of the USB host controller. Some more sophisticated payloads even jump air gaps,so your devices that have no network device or connection can be infected if they have a microphone. BadBIOS and BadUSB are attacks that can do these things,and are old news already. You basically can assume all devices have backdoors built in or if they dont,they will have one added if interested parties want one there.