While the term "deadite" can refer to anything released from a reading of the Necronomicon (Book of the Dead), we will focus on the zombie aspect. While these guys aren't exactly zombies per-se, they are often referred to as such. Really these guys include any person that is posessed by a demonic spirit released by the aforementioned book. They all act human-like but in some instances can move faster than they could in their normal states. These zombies don't really spread by bite and their numbers are only as big as the number of spirits that exist to posess people. Their features do take on a decayed look despite the fact that they are living, but that tends to be common with demon posession lore. As for how to destroy them? Well...dismemberment is really the best way to go.