The corruption occured in 2030, when A fluid called bio turned people into monsters. Usually, it takes a lot of it to fully infect a living organism. But once an organisms dies, they are very easy to infect. This corruption caused 90% of the population to disappear. The man who invented this fluid only saw it as improving mankind. This caused an extra 5% of the population to go out, leaving five percent of humanity to survive. There are 5 stages to infected, 5 being the highest. Try to survive.