Corrupted Blood incident

The Corrupted Blood incident (or World of Warcraft pandemic[1][2]) was a virtual pandemic in the MMORPG World of Warcraft, which began on September 13, 2005, and lasted for one month.[3] The epidemic began with the introduction of the new raid Zul'Gurub and its end boss Hakkar the Soulflayer. When confronted and attacked, Hakkar would cast a hit point-draining and highly contagious debuff spell called "Corrupted Blood" on players.

The Corrupted Blood debuff being spread among characters in Ironforge, one of World of Warcraft's in-game cities.

The spell, intended to last only seconds and function only within the new area of Zul'Gurub, soon spread across the virtual world by way of an oversight that allowed pets and minions to take the affliction out of its intended confines. By both accidental and then purposeful intent, a pandemic ensued that quickly killed lower-level characters and drastically changed normal gameplay, as players did what they could do to avoid infection. Despite measures such as programmer-imposed quarantines, and the players' abandoning of densely populated cities (or even just not playing the game), it lasted until a combination of patches and resets of the virtual world finally controlled the spread.

The conditions and reactions of the event attracted the attention of epidemiologists for its implications of how human populations could react to a real-world epidemic.


The epidemic began on September 13, 2005, when Blizzard introduced a new raid called Zul'Gurub into the game as part of a new update. Its end boss, Hakkar the Soulflayer, could affect a set number of players by applying a contagious debuff called Corrupted Blood, which was countered by players spreading out around the area, away from each other. However, Corrupted Blood could be passed on between any nearby characters, and would kill characters of lower levels in a few seconds, while higher level characters could keep themselves alive. It would disappear as time passed or when the character died.[2]

Due to a programming oversight, when hunters or warlocks dismissed their pets, those pets would keep any active debuffs when summoned again. Non-player characters could contract the debuff, and could not be killed by it but could still spread it to players; in effect, this turned them into asymptomatic carriers and a form of vector for the debuff.[4] At least three of the game's servers were affected. The difficulty in killing Hakkar may have limited the spread of the disease. Discussion forum posters described seeing hundreds of bodies lying in the streets of the towns and cities. Deaths in World of Warcraft are not permanent, as characters are resurrected shortly afterward.[5] However, dying in such a way is disadvantageous to the player's character and incurs inconvenience.[6]

During the epidemic, normal gameplay was disrupted. The major towns and cities were abandoned by the population as panic set in and players rushed to evacuate to the relative safety of the countryside, leaving urban areas filled with dead player characters.[7]

Player responses varied but resembled real-world behaviors. Some characters with healing abilities volunteered their services, some lower-level characters who could not help would direct people away from infected areas, some characters would flee to uninfected areas, and some characters attempted to spread the disease to others.[4] Players in the game reacted to the disease as if there was a real risk to their well-being.[8] Blizzard Entertainment attempted to institute a voluntary quarantine to stem the disease, but it failed, as some players didn't take it seriously, while others took advantage of the pandemic.[4] Despite certain security measures, players overcame them by giving the disease to summonable pets.[9]

Blizzard was forced to fix the problem by instituting hard resets of the servers and applying quick fixes.[5] The plague ended on October 8, 2005, when Blizzard made pets unable to be affected by Corrupted Blood, thereby rendering it unable to exist outside of Zul'Gurub.[10]


At the time, World of Warcraft had more than two million players all over the world.[11] Before Blizzard Entertainment commented on the outbreak, there was debate whether it was intentional or a glitch.[5] On Blizzard's forums, posters were commenting about how it was a fantastic world event, and calling it "the day the plague wiped out Ironforge."[12] An editor of a World of Warcraft fan site described it as the first proper world event.[5] After the incident began, Blizzard received calls from angry customers complaining about how they just died.[12] Some players abandoned the game altogether until the problem was fixed.[13] The hard resets were described as a "blunt ending" by Gamasutra.[4]

The people who spread the disease out of malice were described by Security Focus editor Robert Lemos as terrorists of World of Warcraft.[14]

Jeffrey Kaplan—a game designer for World of Warcraft—stated that it gave them ideas for possible real events in the future.[12] Brian Martin—independent security consultant for World of Warcraft—commented that it presented an in-game dynamic that was not expected by players or Blizzard developers and that it reminds people that even in controlled online atmospheres, unexpected consequences can occur. He also compared it to a computer virus, stating that while it is not as serious, it also reminds people of the impact computer code can have on them, and they're not always safe, regardless of the precautions they take.[14]

Great Zombie Plague of '08Edit

During one week of October 2008, a zombie plague was spread to promote the second World of Warcraft expansion, Wrath of the Lich King, before its release. Unlike Corrupted Blood, this plague was intentional and was dubbed by an authorized representative of Blizzard Entertainment as the "Great Zombie Plague of '08".[15] It was compared to Corrupted Blood by The Sunday Times, which described the zombie plague as being more true-to-life. The plague was contagious, but in contrast to Corrupted Blood, which had 100% transmission to nearby characters, being in the vicinity of a character infected with the zombie plague represented only a small risk of transmission. This meant that encountering a lone zombie was not as dangerous as encountering a large mass of infected individuals.[16] The event—which Blizzard ended on 28 October—earned the company both praise and criticism from its fans.[17]

Green fireEdit

On 12 January 2017, lasting for a day until a hotfix was released by Blizzard,[18] a plague involving a debuff called Burn, that increasingly damaged players over time, started in a boss area. The debuff could be passed between players of the same faction and could kill low-level players in a few seconds.[19] It's believed that the debuff had been taken out of the boss area by a pet. During the incident Blizzard gamemasters "disinfected" players and kept the plague under control.[20]

Models for real-world researchEdit

Model for epidemic researchEdit

In March 2007, Ran D. Balicer, an epidemiologist physician at the Ben-Gurion University of the Negev in Beersheba, Israel, published an article in the journal Epidemiology that described the similarities between this outbreak and the then-recent SARS and avian influenza outbreaks. Dr. Balicer suggested that role-playing games could serve as an advanced platform for modeling the dissemination of infectious diseases.[21] In a follow-up article in the journal Science, the game Second Life was suggested as another possible platform for these studies.[22] The Centers for Disease Control and Prevention contacted Blizzard Entertainment and requested statistics on this event for research on epidemics, but was told that it was a glitch.[12]

The Corrupted Blood incident was described as a fascinating yet accidental case study of modeling disease origins and control at the Games for Health conference in Baltimore, Maryland by Gamasutra.[4] They compared it to a real-life epidemic, in that it originated in a remote, uninhabited region and was carried by travelers to larger regions; hosts were both human and animal, comparing it to the avian flu; was passed through close contact; and there were people, in this case non-playable characters, who could contract it but were asymptomatic.[4] However, there were elements that differed from a real-world epidemic, including an indicator for carriers that they have the disease and how much risk they are at, which cannot be done in the real world.[4] One aspect of the epidemic that was not considered by epidemiologists in their models was curiosity, describing how players would rush into infected areas to witness the infection and then rush out. This was paralleled to real-world behavior, specifically with how journalists would cover an incident, and then leave the area.[4]

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.[23][24] Subsequently, she co-authored a paper in Lancet Infectious Disease discussing the epidemiological and disease modeling implications of the outbreak, along with Eric Lofgren, a University of North Carolina graduate student.[25] She spoke at the 2008 Games for Health conference in Baltimore, Maryland and the 2011 Game Developers Conference about the incident and how massively multiplayer online populations could solve the problems inherent with more traditional models of epidemics.[4][26]

Fefferman added that the three base models have their strengths and weaknesses, but make significant behavioral assumptions. She also compared Corrupted Blood to a drug trial with mice—"a real good first step." She stated, "These are my mice [and] I want this to be my new experiment setup." She expressed an interest in designing new diseases, perhaps non-fatal ones, to be introduced to the game so she could study how risk is viewed, how rumors would spread, and how public health notices are handled. She added that Blizzard made such notices in the original outbreak, but kept changing its position as it could not effectively deal with the problem. She commented that she did not believe it would ruin gameplay, as World of Warcraft dealt with health challenges in combat, and that games set in medieval times had such health risk. She argued that if researchers and developers worked together, it could be fun. While Blizzard was initially excited about the proposition, it became less outwardly excited over time, though never rejected it. She has been in contact with other developers, hoping to conduct the simulation in games similar to World of Warcraft.[4]

Dr. Gary Smith, professor of population biology and epidemiology at the University of Pennsylvania, commented that very few mathematical models of disease transmission take host behavior into account, but also questioned how representative of real life a virtual model could be. He stated that while the characteristics of the disease could be defined beforehand, the study is just as observational as one conducted on a real-life disease outbreak. However, he added that one could argue that the proposal could give an opportunity for a study that epidemiologists may never have.[8] Neil Ferguson, director of the MRC Centre for Global Infectious Disease Analysis at Imperial College, London, felt skeptical of the idea, commenting that such a study could not properly mimic genuine behavior. Using the zombie plague used to promote World of Warcraft: Wrath of the Lich King before its release as an example, players would intentionally become infected to gain zombie powers. He added that characters could also regenerate, meaning there was low risk in becoming infected. He felt that while online games such as World of Warcraft could be set up to help scientists study epidemics, it will always be limited as their primary use is for entertainment.[17]

Model for terrorism researchEdit

In an analysis of the Corrupted Blood incident, Charles Blair, deputy director of the Center of Terrorism and Intelligence Studies, said that World of Warcraft could provide a powerful new way to study how terrorist cells form and operate. While his organization already uses computer models to study terrorists' tactics, Blair explained that because World of Warcraft involves real people making real decisions in a world with controllable bounds, it could provide a more realistic models for military intelligence analysts.[9]

Yale University terrorism expert Stuart Gottlieb admitted that while the outbreak was interesting and relevant to the times, he would not base a counter-terrorism strategy on a video game. Gottlieb expressed skepticism that analyzing the incident could shed light on the complex underlying causes of terrorism in the real world, as the stakes for both terrorists and civilians are lowered in a virtual setting. However, as commented by the editor of the article, "the biggest weakness for using a game as an analytical tool is that death in World of Warcraft is a nuisance at most".[9]

Blizzard has maintained a position that World of Warcraft is first and foremost a game, and that it was never designed to mirror reality or anything in the real world.[9]

Comparison to the COVID-19 pandemicEdit

The Corrupted Blood incident has been compared to the COVID-19 pandemic, and epidemiologists who studied the Corrupted Blood outbreak are using the research from the incident to better understand COVID-19's spread - primarily its sociological factors.[27][28][29][30][31] Dr. Eric Lofgren, an epidemiologist and co-author of a research paper about Corrupted Blood, stated in an interview with PC Gamer that "When people react to public health emergencies, how those reactions really shape the course of things. We often view epidemics as these things that sort of happen to people. There's a virus and it's doing things. But really it's a virus that's spreading between people, and how people interact and behave and comply with authority figures, or don't, those are all very important things. And also that these things are very chaotic. You can't really predict 'oh yeah, everyone will quarantine. It'll be fine.' No, they won't."[27][28][29][30] Griefing, such as players intentionally spreading Corrupted Blood to others, was one of the aspects of the Corrupted Blood study that has been criticized as lacking a real-world basis; Dr. Lofgren expressed in the wake of the COVID-19 pandemic that "one of the critiques we got from a lot of people, both gamers and scientists, was over this idea of griefing, ... How griefing isn't really analogous to anything that takes place in the real world. People aren't intentionally getting people sick. And they might not be intentionally getting people sick, but wilfully ignoring your potential to get people sick is pretty close to that. You start to see people like 'oh this isn't a big deal, I'm not going to change my behavior.' ... Epidemics are a social problem... Minimizing the seriousness of something is sort of real-world griefing."[27]

The Corrupted Blood incident was abrupt and far-reaching; Dr. Lofgren expressed that this abruptness is a property of a real pandemic, stating "Corrupted Blood was this unexpected black swan event. We treat this [COVID-19] as if it's unexpected, but nature is really good at getting people sick".[27][30] Dr. Nina Fefferman, a co-author of the Corrupted Blood study, expressed that the incident particularly exemplified "how people perceive threats and how differences in that perception can change how they behave", and how people discuss a threat on social media, stating that "A lot of my work since then has been in trying to build models of the social construction of risk perception and I don't think I would have come to that as easily if I hadn't spent time thinking about the discussions WoW players had in real time about Corrupted Blood and how to act in the game based on the understanding they built from those discussions."[27][28][30]

See alsoEdit


  1. ^ "The weird World of Warcraft pandemic of 2005". 6 March 2020.
  2. ^ a b Elker, Jhaan. "World of Warcraft experienced a pandemic in 2005. That experience may help coronavirus researchers". Washington Post. ISSN 0190-8286. Retrieved 2021-01-04.
  3. ^ Messner, Steven (August 26, 2019). "How Blizzard coped with World of Warcraft's blood plague and other early disasters". PC Gamer. Retrieved 28 October 2021.
  4. ^ a b c d e f g h i j Orland, Kyle (2008-05-20). "GFH: The Real Life Lessons Of WoW's Corrupted Blood". Gamasutra. Game Developer. Archived from the original on 2019-04-13. Retrieved 2019-04-13.
  5. ^ a b c d Ward, Mark (2005-09-22). "Deadly plague hits Warcraft world". BBC News Online. BBC. Archived from the original on 2019-03-31. Retrieved 2019-04-13.
  6. ^ McNamara, Tom (2005-09-22). "World of Warcraft Gets Plagued". IGN. News Corporation. Archived from the original on 2019-04-13. Retrieved 2019-04-13. In-game disease spreads throughout the realm.
  7. ^ Marshall, Andrew (2009-04-27). "Online 'blood plague' offers lessons for pandemics". Reuters. Archived from the original on 2019-04-13. Retrieved 2019-04-13.
  8. ^ a b "Virtual game is a 'disease model'". BBC News Online. BBC. 2007-08-21. Archived from the original on 2009-01-27. Retrieved 2019-04-13. An outbreak of a deadly disease in a virtual world can offer insights into real life epidemics, scientists suggest.
  9. ^ a b c d Thier, David (2008-03-20). "World of Warcraft Shines Light on Terror Tactics". Archived from the original on 2019-08-05. Retrieved 2019-04-13.
  10. ^ Bove, Kate (March 29, 2020). "What World of Warcraft Taught Us About Real-World Pandemics 15 Years Ago". Retrieved October 28, 2021.
  11. ^ Smith, Tony (2005-09-21). "World of Warcraft Plague Swamps Servers". The Register. Archived from the original on 2018-10-22. Retrieved 2019-04-13.
  12. ^ a b c d "Looking Back... World of Warcraft". Computer and Video Games. 2005-01-04. Archived from the original on 2014-02-19. Retrieved 2019-04-13.
  13. ^ "Virtual worlds, real science: epidemiologists, social scientists flock to online world". Science News. 2007-10-27. Archived from the original on 2019-04-13. Retrieved 2019-04-13.
  14. ^ a b Lemos, Robert (2005-09-27). "Digital plague hits online game World of Warcraft". Security Focus. Archived from the original on 2019-11-02. Retrieved 2019-04-13.
  15. ^ Tigole (2008-10-27). "Regarding the Zombie Plague…". Blizzard Entertainment. Archived from the original on 2010-10-19. Retrieved 2019-04-13.
  16. ^ Henderson, Mark (2008-10-28). "Analysis: Absence of risk limits parallels with real life". The Sunday Times. News International. ISSN 0956-1382. Archived from the original on 2019-04-13. Retrieved 2010-10-19. Why avoid anything like the plague if you can just come back to life?
  17. ^ a b Ahmed, Murad (2008-10-28). "World of Warcraft plague halted by Blizzard". The Sunday Times. News International. ISSN 0956-1382. Archived from the original on 2019-04-13. Retrieved 2019-04-13. The Warcraft's authorities have acted to control a virtual plague they released into the popular online game last week
  18. ^ "Hotfixes January 13". 2017-01-13. Archived from the original on 2019-03-28. Retrieved 2019-04-13.
  19. ^ "Green fire killing everyone". 2017-01-12. Archived from the original on 2019-03-28. Retrieved 2019-04-13.
  20. ^ "WoW, another blood plague". 2017-01-12. Retrieved 2019-04-13.
  21. ^ Balicer, Ran (2005-10-05). "Modeling Infectious Diseases Dissemination Through Online Role-Playing Games". Epidemiology. 18 (2): 260–261. doi:10.1097/01.ede.0000254692.80550.60. PMID 17301707.
  22. ^ "Playing With Epidemics". Science. 316 (5827): 961. 2007-05-18. doi:10.1126/science.316.5827.961a. S2CID 220092978.
  23. ^ Sydell, Laura (2005-10-05). "'Virtual' Virus Sheds Light on Real-World Behavior". NPR. Archived from the original on 2019-08-25. Retrieved 2019-04-13.
  24. ^ Bannerman, Lucy (2007-08-21). "How a computer game glitch could help to fight off global pandemic". The Times. Archived from the original on 2018-07-22. Retrieved 2019-04-13.
  25. ^ Lofgren, Eric T.; Fefferman, Nina H. (2007-09-01). "The untapped potential of virtual game worlds to shed light on real world epidemics". The Lancet Infectious Diseases. 7 (9): 625–629. doi:10.1016/S1473-3099(07)70212-8. PMID 17714675. Archived from the original on 2010-01-24. Retrieved 2019-04-13.
  26. ^ Graft, Kris (2011-02-28). "GDC 2011: An Epidemiologist's View Of World Of Warcraft's Corrupted Blood Plague". Gamasutra. Archived from the original on 2019-04-13. Retrieved 2019-04-13.
  27. ^ a b c d e Fenlon, Wes (March 13, 2020). "The researchers who once studied WoW's Corrupted Blood plague are now fighting the coronavirus". PC Gamer. Future plc.
  28. ^ a b c Maskell, Ryan (March 14, 2020). "The doctors who studied WoW's virtual blood plague warn of the reality of coronavirus". PCGamesN. Network N.
  29. ^ a b Hruska, Joel (March 16, 2020). "Researchers Are Dusting Off WoW's Corrupted Blood Plague to Understand Coronavirus Infections". ExtremeTech. Ziff Davis Media.
  30. ^ a b c d Ouellette, Jennifer (March 16, 2020). "What a WoW virtual outbreak taught us about how humans behave in epidemics". Ars Technica. Condé Nast.
  31. ^ Krotoski, Aleks (March 31, 2020). "Corrupted Blood: what the virus that took down World of Warcraft can tell us about coronavirus". BBC Science Focus. Immediate Media Company.

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