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 [2]. In a follow-up article in the Journal Science, the game Second Life was suggested as another possible platform for these studies.[3]

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.[4][5]

In addition, Centers for Disease Control and Prevention had requested statistics on this event for research on epidemics.