I just got an AUP notification stating that I downloaded a movie that I have no idea of what it is even about. How do I deal with this and prevent it from happening again. Nobody else has access to my modem or internet.

They should have the time, item, and IP address of the AUP in question. Do you have Hotspot enabled? I always wondered who it tracked to when someone goes on someone else hotspot. The IP of the hotspot or the username signed in with? It doesn't seem to track bandwidth to the username, so I assume the IP.