The threats that NORAD faces in the cyberdomain are the same that pretty much every citizen faces. Asymmetrically, first you have those who break the law, the hackers. They try to establish their prestige by how much damage they can do. That's in the realm of law enforcement. Then you have the terrorist organizations, who may want to impose harm through an attack on our cybersystem. Then you have the state actors, who mainly try to get information on how we operate and how to break the system so that, in the event of confrontation, they could either create a diversion or make us blind.
As I said previously, NORAD operates with cybersystems in a contested cyber environment.