Corrupted Blood incident

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

The Corrupted Blood incident was a virtual pandemic in the MMORPG World of Warcraft, which began on September 13, 2005, and lasted for one week. 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 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 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 of Zul'Gurub, could affect players by using a debuff called Corrupted Blood which did a significant amount of damage to the player over time. The disease 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. Due to a programming error, 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 disease carriers and a form of vector for the debuff.[1] 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.[2] However, dying in such a way is disadvantageous to the player's character and incurs inconvenience.[3]

During the epidemic, normal gameplay was disrupted. 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.[1] Players in the game reacted to the disease as if there were real risk to their well-being.[4] 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 pandemonium.[1] Despite certain security measures, players overcame them by giving the disease to summonable pets.[5] Blizzard was forced to fix the problem by instituting hard resets of the servers and applying quick fixes.[2]

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 to the brim with corpses, and the city streets literally white with the bones of the dead.[6]

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.


At the time, World of Warcraft had more than two million players all over the world.[7] Before Blizzard Entertainment commented on the outbreak, there was debate whether it was intentional or a glitch.[2] 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."[8] An editor of a World of Warcraft fan site described it as the first proper world event.[2] After the incident began, Blizzard received calls from angry customers complaining about how they just died.[8] Some players abandoned the game altogether until the problem was fixed.[9] The hard resets were described as a "blunt ending" by Gamasutra.[1]

The people who spread the disease out of malice were described by Security Focus editor Robert Lemos as terrorists of World of Warcraft.[10] He commented that this might be the first time a disease passed from player to player in a game.[10]

Jeffrey Kaplan—a game designer for World of Warcraft—stated that it gave them ideas for possible real events in the future.[8] 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.[10]

Great Zombie Plague of '08[edit]

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".[11] 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.[12] The event—which Blizzard ended on 28 October—earned the company both praise and criticism from its fans.[13]

Green fire[edit]

On 12 January 2017, lasting for a day until a hotfix was released by Blizzard [14], a plague started, involving a debuff from the second boss in the instance Sunwell Plateau - Brutallus, called Burn which damages players over time, specifically doing significantly increasing damage. The debuff could be passed from player to player of the same faction within 2 yards, and would kill low level players[15] in a few seconds, while higher level players would manage to keep themselves alive. It would disappear in 1 minute or when the player died. The debuff would reset its timer if an ally was infected. It was believed that the debuff had been taken out of the instance using a hunter pet, which had the effect on. During the incident, Blizzard gamemasters disinfected players and kept the plague under control[16] by warning groups, such as "Green Fire Parade", who were spreading the plague from Stormwind across Goldshire. As in previous plagues, the green fire had been kept alive by players in many different locations, including Northshire, Goldshire and Stormwind, until a hotfix was released.

Models for real-world research[edit]

Model for epidemic research[edit]

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 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.[17] In a follow-up article in the journal Science, the game Second Life was suggested as another possible platform for these studies.[18] 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.[8]

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.[1] 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.[1] 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.[1] 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.[1]

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.[19][20] 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.[21] 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.[1][22]

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.[1]

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.[4] Neil Ferguson, director of the MRC Centre for Outbreak Analysis and Modelling 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.[13]

Model for terrorism research[edit]

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.[5]

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".[5]

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.[5]


  1. ^ 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. Retrieved 2019-04-13.
  2. ^ a b c d Ward, Mark (2005-09-22). "Deadly plague hits Warcraft world". BBC News Online. BBC. Retrieved 2019-04-13.
  3. ^ McNamara, Tom (2005-09-22). "World of Warcraft Gets Plagued". IGN. News Corporation. Retrieved 2019-04-13. In-game disease spreads throughout the realm.
  4. ^ a b "Virtual game is a 'disease model'". BBC News Online. BBC. 2007-08-21. Retrieved 2019-04-13. An outbreak of a deadly disease in a virtual world can offer insights into real life epidemics, scientists suggest.
  5. ^ a b c d Thier, David (2008-03-20). "World of Warcraft Shines Light on Terror Tactics". Retrieved 2019-04-13.
  6. ^ Marshall, Andrew (2009-04-27). "Online 'blood plague' offers lessons for pandemics". Reuters. Retrieved 2019-04-13.
  7. ^ Smith, Tony (2005-09-21). "World of Warcraft Plague Swamps Servers". The Register. Retrieved 2019-04-13.
  8. ^ 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.
  9. ^ "Virtual worlds, real science: epidemiologists, social scientists flock to online world". Science News. 2007-10-27. Retrieved 2019-04-13.
  10. ^ a b c Lemos, Robert (2005-09-27). "Digital plague hits online game World of Warcraft". Security Focus. Retrieved 2019-04-13.
  11. ^ Tigole (2008-10-27). "Regarding the Zombie Plague…". Blizzard Entertainment. Archived from the original on 2010-10-19. Retrieved 2019-04-13.
  12. ^ Henderson, Mark (2008-10-28). "Analysis: Absence of risk limits parallels with real life". The Sunday Times. News International. ISSN 0956-1382. Retrieved 2010-10-19. Why avoid anything like the plague if you can just come back to life?
  13. ^ a b Ahmed, Murad (2008-10-28). "World of Warcraft plague halted by Blizzard". The Sunday Times. News International. ISSN 0956-1382. Retrieved 2019-04-13. The Warcraft's authorities have acted to control a virtual plague they released into the popular online game last week
  14. ^ "Hotfixes January 13". 2017-01-13. Retrieved 2019-04-13.
  15. ^ "Green fire killing everyone". 2017-01-12. Retrieved 2019-04-13.
  16. ^ "WoW, another blood plague". 2017-01-12. Retrieved 2019-04-13.
  17. ^ 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. Retrieved 2019-04-13.
  18. ^ "Playing With Epidemics". 316 (5827). 2007-05-18: 961. doi:10.1126/science.316.5827.961a.
  19. ^ Sydell, Laura (2005-10-05). "'Virtual' Virus Sheds Light on Real-World Behavior". NPR. Retrieved 2019-04-13.
  20. ^ Bannerman, Lucy (2007-08-21). "How a computer game glitch could help to fight off global pandemic". The Times. Retrieved 2019-04-13.
  21. ^ 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. Retrieved 2019-04-13.
  22. ^ Graft, Kris (2011-02-28). "GDC 2011: An Epidemiologist's View Of World Of Warcraft's Corrupted Blood Plague". Gamasutra. Retrieved 2019-04-13.

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