In 2005, a virtual plague in World of Warcraft became an accidental laboratory for studying how real pandemics spread.

The Corrupted Blood incident began on September 13, 2005, following the release of the Zul'Gurub raid in World of Warcraft. The final boss, Hakkar the Soulflayer, cast a 'Corrupted Blood' spell that drained health and spread rapidly between players. Although designed to remain confined to the dungeon, players discovered that their in-game pets could carry the virus into the game's capital cities.Once the virus reached densely populated hubs like Ironforge and Orgrimmar, it spread uncontrollably, killing lower-level players within seconds. Blizzard Entertainment, the game's developer, struggled to contain the outbreak despite attempting quarantines and server resets. The chaos attracted the attention of epidemiologists, including Dr. Nina Fefferman and Dr. Eric Lofgren, who published a paper analyzing the event in The Lancet Infectious Diseases in 2007.The researchers found that player behavior introduced a level of realism absent from traditional computer models. They documented 'the curious case of the curious,' where players deliberately traveled to infected areas to witness the chaos, and the actions of 'malicious actors' who intentionally spread the disease. These observations illuminated how irrational human behavior and social connectivity can dramatically alter the trajectory of real epidemics.The incident proved so significant that organizations like the CDC later referenced it when discussing disaster preparedness and social modeling. It remains one of the most striking examples of an accidental simulation yielding legitimate scientific value. Blizzard ultimately ended the event by performing a hard reset of the game servers and modifying the spell's mechanics.