Corrupted Blood
Corrupted Blood was a virtual plague that infected characters in the computer game World of Warcraft, spreading rapidly from character to character. Its resemblance to real-life disease epidemics drew international attention in the news.

# Information
The epidemic began on September 13, 2005 when Blizzard Entertainment, the developer of World of Warcraft, introduced a new instance called Zul'Gurub into the game as part of patch 1.7. Inside this instance was a boss named Hakkar the Soulflayer, alluded to as the "blood god". Players who fought Hakkar were affected by his debuff (a spell which has a negative effect over a fixed period of time). The debuff, in this case, was Corrupted Blood, a spell that caused 250300 points of damage (compared to the average health of 2500-5000 for a player of the highest level, and with those at the mid-levels having about 1500) every few seconds to the afflicted player. The affliction was passed on to any players standing too close to infected players. While the curse would kill most lower-level players in a matter of seconds, higher-level players could keep themselves alive (via healing spells, having high stamina, or other means) long enough to spread the disease around the immense landscape inside the game. Death caused by the debuff did not cause any durability penalty, unlike most other causes of death in the game. NPCs, combat pets, and non-combat pets were key in spreading the plague.
The disease would eventually go away as time passed or when the infected character died.  The only way that a player was able to bring the disease outside of Zul'Gurub was by allowing a pet to get the debuff, dismissing the pet in less than five seconds, then summoning it in a populated area. (When dismissed, the pet retains the debuff and the timer of the debuff is paused.) This debuff transmission technique was first seen with the "living bomb" debuff from Baron Geddon in Molten Core.

# Scale and effect of Corrupted Blood
After a few days, Corrupted Blood had become World of Warcraft's version of the Black Death, rendering entire cities uninhabitable and causing players to avoid large clusters of other players, and in many cases, causing players to avoid major cities altogether.
Due to the curse's peculiar behavior, it was never meant to leave Zul'Gurub - the ability to infect pets and NPCs was a side effect unconsidered by the developers. The intended behavior involves the final boss fight with Hakkar. Every so often, Hakkar will cast this debuff on a random player, effectively forcing players to be spread apart, or in the case of melee classes, to move away from Hakkar before spreading it to the other melee classes. Blizzard Entertainment tried several times to fix the problem, including imposing quarantine on certain places.  This "plague" was eventually "cured" by changing the mechanics of the Hakkar encounter to eliminate the spreading of the effect from player to player.  Hakkar still has an ability called Corrupted Blood, but it now takes the form of a red bolt launched at a random player fighting the boss.  The player and those nearby take damage, and receive a heavy damage over time, but the effect no longer spreads further.
Due to the large scale outbreak of the "plague" (some servers had half of their players infected), it drew wide attention from the media.
In March 2007, Ran D Balicer, an epidemiologist physician at the Ben-Gurion University in Israel, published an article in the Journal Epidemiology describing the similarities between this outbreak and the recent SARS and avian influenza outbreaks. 
Dr Balicer suggested role-playing games could serve as an advanced platform for modeling the dissemination of infectious diseases . In a follow-up article in the Journal Science, the game Second Life was suggested as another possible platform for these studies.
In August 2007, Nina Fefferman, a Tufts University assistant research professor of public health and family medicine, called for research on this incident, citing the resemblances with biological plagues. Some scientists want to study how people would react to environmental pathogens, by using the virtual counterpart as a point of reference.
In addition, Centers for Disease Control and Prevention had requested statistics on this event for research on epidemics.