Zombies are the sufferers of a degenerated form of vampirism. The curse retains enough power to animate their dead bodies, but not enough to preserve them against decay or keep their minds intact. Vampires who are 6 generations descended from Dracula sire zombie lords instead of normal vampires. Zombie lords sire zombies and zombies sire more zombies. Zombie lords have the power to control zombies.
Zombies are stronger than humans and can only be killed by destroying the brain or seperating the head from the body(even then the head continues to snap at people's ankles). They are however, slow, clumsy and stupid which makes them easy to evade in small numbers. However, even highly skilled warriors can be brought down by large groups of zombies, especially if they get surrounded.
Zombie bites, as well as transferring a curse, also transfer a hideous virulent virus which usually kills the victim with about a day or so. It is worth noting that even if the victim dies of other causes, he will rise as a zombie so long as the virus was still in his system.