# The Corrupted Blood Incident - Event: Incident - Date: September 13 – October 8, 2005 - Houses: Blizzard Entertainment - Canonical: https://www.lanternhall.org/culture/corrupted-blood-incident/ > In 2005 a raid boss's blood curse escaped its dungeon via players' pets and swept World of Warcraft's cities, leaving streets white with bones and handing epidemiologists an accidental pandemic to study. **Why it matters:** An accidental virtual plague showed how real people behave in an outbreak (fleeing, helping, spreading it on purpose) and became a touchstone for research into games as models of human behavior in epidemics. ## Quick answers **What was The Corrupted Blood Incident?** In 2005 a raid boss's blood curse escaped its dungeon via players' pets and swept World of Warcraft's cities, leaving streets white with bones and handing epidemiologists an accidental pandemic to study. **When did The Corrupted Blood Incident happen?** September 13 – October 8, 2005. **Why did The Corrupted Blood Incident matter?** An accidental virtual plague showed how real people behave in an outbreak (fleeing, helping, spreading it on purpose) and became a touchstone for research into games as models of human behavior in epidemics. ## What happened By September 2005 the [MMORPGs](https://www.lanternhall.org/atlas/mmorpg/) *[World of Warcraft](https://www.lanternhall.org/works/world-of-warcraft/)* was less than a year old and already had more than four million subscribers. To keep its most dedicated players busy, [Blizzard Entertainment](https://www.lanternhall.org/houses/blizzard-entertainment/) kept adding [raids](https://www.lanternhall.org/lexicon/raid/), and on September 13 it opened Zul'Gurub, a jungle temple designed for 20 players. Its final boss, the blood god Hakkar the Soulflayer, used a debuff called Corrupted Blood: a curse that drained health rapidly from an infected character and jumped to anyone standing nearby. It was meant to be a tactical puzzle, lasting only seconds and confined to the raid's [Instanced dungeon](https://www.lanternhall.org/lexicon/instance/), and to vanish when Hakkar died. There was a loophole. Hunters could dismiss their animal companions mid-fight and summon them later, and the game did not clear the debuff from a dismissed pet. When players finished the raid, teleported home to repair their gear, and resummoned their pets in crowded capitals such as Orgrimmar and Ironforge, the pets brought Corrupted Blood with them. [Non-player characters](https://www.lanternhall.org/lexicon/non-player-character/) could catch it too; they could not die, so they became asymptomatic carriers. For a high-level hero the plague was dangerous; for anyone below about level 50 it was nearly instant death. Forum posts described cities "filled to the brim with corpses," their streets white with the skeletons of the dead. Players reacted exactly as people do. Some fled to the countryside and self-isolated. Low-level characters stood outside infected towns warning others away, and one player became a sort of town crier, shouting news of outbreaks. [Healers](https://www.lanternhall.org/lexicon/holy-trinity/) rushed into cities as volunteer first responders, where they often caught the disease themselves, and their spells frequently just kept the infected alive and contagious longer. Rumor and misinformation spread on forums; some players insisted the plague was a deliberate event. And griefers deliberately infected themselves and ran into crowds for the fun of watching people "run away screaming." Blizzard acknowledged the problem on September 16 and tried quarantine zones, which players evaded, and rolling server restarts, after which outbreaks flared up again when players returned. After about a week it performed hard resets of the servers, and on October 8 a patch made pets immune to Corrupted Blood. ## Why it mattered The incident was a software bug, but it produced something epidemiologists had never had: an outbreak involving millions of real people making real choices, with no risk to anyone's health. Mathematical disease models must assume how people will behave; here people simply behaved. In an article in *Epidemiology*, Ran Balicer of Ben-Gurion University compared the pets to the ducks that silently carried avian influenza; the game's fast travel was likewise compared to the role of air travel in spreading SARS. In September 2007, Eric Lofgren and Nina Fefferman published "The untapped potential of virtual game worlds to shed light on real world epidemics" in *The Lancet Infectious Diseases*, arguing that online games could help researchers incorporate human behavior, including curiosity, altruism, and malice, into outbreak modeling. Fefferman observed that players "seemed to really feel they were at risk." Skeptics pointed to the differences. A character who dies in *World of Warcraft* simply revives, so the stakes are low; Corrupted Blood spread far faster than any real pathogen; and infected characters gained no immunity. Players, as one researcher noted, are encouraged in games to behave in ways they never would offline. According to later accounts, the Centers for Disease Control and Prevention even asked Blizzard about the outbreak's data, only to learn that there was none, because it had been an accident. ## Legacy Blizzard learned to stage plagues on purpose. A zombie outbreak heralded *Wrath of the Lich King* in 2008, and another came with *Shadowlands* in 2020; [BioWare's](https://www.lanternhall.org/houses/bioware/) *Star Wars: The Old Republic* staged its own Rakghoul Plague in 2012, which its lead designer said was inspired by Corrupted Blood. Zul'Gurub itself was removed in 2010 and rebuilt as a five-player dungeon in 2011, and when it returned in *World of Warcraft Classic* in 2020, the code already included the fix. The event took on a second life during the COVID-19 pandemic, when journalists and researchers, including Lofgren, revisited it to discuss superspreading, first responders overwhelmed by patients, and people who ignored quarantine. Alongside [Leeroy Jenkins](https://www.lanternhall.org/culture/leeroy-jenkins/), it is one of the defining legends of early *World of Warcraft* and one of the clearest demonstrations that [Online Worlds: From MUD1 to World of Warcraft](https://www.lanternhall.org/chronicle/online-worlds/) are social laboratories as well as games. ## Facts - Corrupted Blood was cast by Hakkar the Soulflayer, boss of the 20-player Zul'Gurub raid added on September 13, 2005. - The debuff escaped because hunters' pets, dismissed while infected, carried it out of the raid when they were summoned again. - Non-player characters could carry the infection without dying, acting as asymptomatic carriers. - Griefers deliberately caught the plague and ran into crowded cities to spread it, a behavior researchers compared to Typhoid Mary. - Blizzard tried quarantines and rolling restarts before resetting servers; an October 8 patch made pets immune. - Eric Lofgren and Nina Fefferman analyzed the outbreak in The Lancet Infectious Diseases in September 2007. ## Sources and further reading - [Wikipedia](https://en.wikipedia.org/wiki/Corrupted_Blood_incident) - [Lofgren & Fefferman, The Lancet Infectious Diseases (2007), PubMed](https://pubmed.ncbi.nlm.nih.gov/17714675/) --- From The Lantern Hall (https://www.lanternhall.org/), a museum of fantasy literature and roleplaying games.