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Corrupted Blood plague incident
Main article: Corrupted Blood incident
The Corrupted Blood plague incident was one of the first events to affect entire servers. Patch 1.7 saw the opening of Zul'Gurub, the game's first 20-player raid dungeon where players faced off against an ancient tribe of jungle trolls under the sway of the ancient Blood God, Hakkar the Soulflayer. Upon engaging Hakkar, players were stricken by a debuff called "Corrupted Blood" which would periodically sap their life. The disease would also be passed on to other players who were simply standing close to an infected person. Originally this malady was confined within the Zul'Gurub instance but made its way into the outside world by way of hunter pets or warlock minions that contracted the disease.
Within hours Corrupted Blood had infected entire cities such as Ironforge and Orgrimmar 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.[67]

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