World Of Warcraft Girl

Within hours, Corrupted Blood had completely infected major cities because of their high player concentrations. Low-level players were killed in seconds by the high-damage disease. Eventually Blizzard fixed the issue so that the plague could not exist outside of Zul'Gurub.
The Corrupted Blood plague so closely resembled the outbreak of real-world epidemics that scientists are currently looking at ways MMORPGs or other massively distributed systems can model human behavior during outbreaks. The reaction of players to the plague closely resembled previously hard-to-model aspects of human behavior that may allow researchers to more accurately predict how diseases and outbreaks spread amongst a population.