Reanimating the Dead
The rising of the first zombies occurred en masse, in mass graves where the victims of RSSN were buried. Once again, an alien operations protocol—The Drone Protocol—was to blame.
Nanites duplicated themselves using human tissues. This ate holes in vital organs, eventually killing the host.
To keep their host body operating after organ failure and brain death, the nanite colonies worked to animate their hosts. Eventually, after many attempts, they succeeded. One single nanite colony was able to resuscitate its host body, reanimating it as a drone.
Drones were completely under control of the nanite cluster, lacking all self-awareness or self-will. Drones became the slaves that Conditioning had failed to provide.
The Protocol maintained, or restored, a minimal level of bodily functions: sensory organs, musculature and tendons, and the skeletal system (either repairing damage to the native structures, augmenting the native structures with artificial tissues, or replacing their function entirely). The body of the zombie—as people called the drones—could walk, sense things (that is, the nanites could use the host's organs to do so), and engage in self-defense and basic attacks, but otherwise operated at an extremely low cognitive level compared to the not-yet-dead.
(In fact, this interface with the host’s sensory system is what gave RSSN sufferers their characteristic red eyes: nanites infected the eyes, so they could gather visual data. Their presence in the cochlea, the nasal cavity, and the spinal column was just as important, but not as immediately visible.)
The first nano-zombie broadcast the protocol to all within range. Had it been buried alone in a field, far from any other host, this would have been pointless. It wasn’t. It was part of a mass grave outside Newark, New Jersey. This grave held over a thousand corpses, and several such graves lay close by.
Each corpse had a functioning nanite colony, each corpse was a node, and each corpse reanimated under the control of the nanites. The Drone Protocol was broadcast to each host, and in 24-48 hours after the protocol was first broadcast (the time necessary to restore functionality), the drones went active and tore themselves from the earth. The Newark mass graves were the first instances of mass reanimation, but the phenomenon soon spread.
Once the protocol was loose, it was broadcast from host to host, even to healthy ones. Any host that received the protocol was primed for reanimation upon death, no matter the cause. So, as the living fought the rampaging RSSN victims, each living and infected human they killed reanimated as a drone.
The Drone Protocol could reanimate the dead. More, the protocol could be used to supplement the functioning of live hosts who the phage was killing. As various organs failed, the protocol could replace their functions, keeping the host alive even as the phage ate holes in their major organs.
Gradual Systemic Spongiform Necrosis had arrived, and with it the Carriers.
The Hunger
Zombies hunger for flesh. Not because the host body can digest and extract nutrients from it, but because the nanites can use it to replicate themselves, to keep their host mobile, or to augment its functions with artificial ones.
Drones are driven to find and consume organic tissue from everything but other zombies. Recognition protocols keep them from attacking each other. Instead, they attack the living or Carriers.