Zombie Apocalypse

The world has fallen to a legal virus that turns everyone infected into zombies. Humanity is on the brink of extinction, only 20% of humans survived the infection by building underground cities and towns. In a last ditch effort to destroy the zombies and the virus, the world leaders elected to use all the nuclear weapons, targeting every major landmass. However, not only did this not destroy the virus, or even all the infected, it mutated the virus and made the surface unlivable. Radiation storms have made traveling along the surface incredibly dangerous, not to mention the infected, now mutated by the radiation. The survivors that remain do what they can, building underground gardens and farms. But resources are scarce, so each settlement has a group of brave individuals called "Rangers" that explore the surface for any resources.