The Krippin Virus was genetically engineered from the measles virus by Dr. Alice Krippin as a cure for cancer KV at first appeared to be effective with no side-effects, but over time, the virus began to mutate and cause rabies-like symptoms in its hosts The virus breaks out in December 2009. How the virus escaped from the laboratory is unclear Despite the military's best efforts to contain KV, it eventually mutated into a lethal new strain of measles with a 90% kill rate, and went airborne. KV spread out from Manhattan across the globe, killing 5.4 billion people. Of the 600 million who did not die from the virus, only 12 million were naturally immune to KV; the other 588 million devolved into Darkseekers, who would prey on the surviving humans including those with immunity