The Corrupted Blood incident was a widely reported virtual plague outbreak and video game glitch found in the Blizzard Entertainment computer game World of Warcraft, a massively multiplayer online role-playing game in the Warcraft series. The plague began on September 13, 2005, when an area was introduced in a new update. One boss could cast a spell called Corrupted Blood, which would deal a certain amount of damage over a period of time, and which could be transferred from character to character. It was intended to be exclusive to this area, but players discovered ways to take it out, causing an epidemic across several servers. During the epidemic, some players would help combat the disease by volunteering healing services, while select others would maliciously spread the disease. These people have been compared to real-world disease spreaders, including early AIDS patient Gaëtan Dugas and Typhoid patient Mary Mallon. Blizzard attempted to fix the problem with voluntary quarantines, but most did not take it seriously, forcing Blizzard to do a hard reset of all of its servers for the game. The glitch received mixed reactions. Complaints from players arose quickly after it became widespread and their characters died from this disease. However, some players found the situation fascinating. It has also been described as the first "real world" event in the game. World of Warcraft game designer Jeffrey Kaplan commented that the event caused them to consider similar real events in the game for the future. The resemblance to real-life disease epidemics drew international attention. Epidemiologist Ran D. Balicer published an article in the journal Epidemiology comparing it to SARS and avian influenza outbreaks. He suggested that role-playing games could be used as an advanced platform as a model for the dissemination of infectious diseases. Tufts University assistant research professor of public health and family medicine Nina Fefferman called for research on the incident. She spoke at the Games for Health conference in Baltimore, Maryland, commenting that massively multiplayer online games could solve the problems found in traditional models of epidemics, and that she would like to see a simulated epidemic done in World of Warcraft or another similar game that she could study. The actions of some players was described as terrorism by some, including Charles Blair, deputy director of the Center for Terrorism and Intelligence Studies, who felt that World of Warcraft could provide a new way to study how terrorist cells form and operate.


The epidemic began on 2005-09-13, when Blizzard introduced a new dungeon called Zul'Gurub into the game as part of a new update for the game. Its end boss, Hakkar, could affect players by using a debuff called Corrupted Blood, a disease that damages players over time, this one specifically doing significant damage. The disease could be passed on between any nearby characters, and would kill characters of lower level in a few seconds while higher level characters could keep themselves alive. It would disappear as time passed or when the character died. Players could spread this effect by teleporting out of Zul'Gurub and passing it on to other players. Although the disease was intended as a "short-term, short-range annoyance", some players took advantage of the teleport glitch. Non-playable characters could contract the disease, but were asymptomatic to it and could spread it to others. At least three of the game's servers were affected. One factor that may have limited its spread to some servers is that the boss is difficult to kill. 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 would be resurrected shortly afterward. However, dying in such a way will be disadvantageous to the player's character and consequently it is inconvenient to get the infection. 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 – resembling behaviour attributed to early AIDS patient Gaëtan Dugas and Typhoid patient Mary Mallon. Players in the game reacted to the disease as if there was real risk to their well-being. 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. Despite certain security measures, players overcame them by giving the disease to summonable pets. They were forced to fix the problem by instituting hard resets of the servers and applying "quick fixes". However, reports exist saying that isolated pockets of the plague have broken out.


World of Warcraft, at the time, had more than two million players all over the world. Before Blizzard Entertainment commented on the outbreak, there was debate whether it was intentional or a glitch. 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." It was described as the first proper "world event" by an editor of a World of Warcraft fan site. After the incident began, Blizzard received calls from angry customers complaining about how they just died. Some players abandoned the game altogether until the problem was fixed. The hard resets were described as a "blunt ending" by Gamasutra. The people who spread the disease out of malice were described by Security Focus editor Robert Lemos as terrorists of World of Warcraft. He commented that this may be the first time that a disease has passed between player to player in a game, though Mark Ward, an editor for the BBC's web site, brought up an incident years earlier in the computer game The Sims, where an outbreak from a dirty guinea pig caused many players' characters to catch this disease and lose their lives. Jeffrey Kaplan, the game designer for World of Warcraft, commented that it gave them ideas for possible real events in the future. 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. During one week, a zombie plague was spread to promote the second World of Warcraft expansion, World of Warcraft: Wrath of the Lich King, before its release. Unlike Corrupted Blood, this plague was intentional. It was compared to Corrupted Blood by Times Online, who described the zombie plague as being more true-to-life. The plague was highly 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.

Model for real-world research[]

Model for epidemic research[]

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. In a follow-up article in the journal Science, the game Second Life was suggested as another possible platform for these studies. 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. The Corrupted Blood incident was described as a fascinating, yet accidental, by case study of modeling disease origins and control at the Games for Health conference in Baltimore, Maryland by Gamasutra. 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. 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. 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 rush toward a problem to cover it, and then rush back out. 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. Subsequently she co-authored a paper in the journal "Lancet Infectious Diseases" discussing the epidemiological and disease modeling implications of the outbreak, along with Eric Lofgren, a University of North Carolina graduate student. In May 2008, she spoke at the Games for Health conference in Baltimore, Maryland about how massively multiplayer online populations could solve the problems inherent with more traditional models of epidemics. 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 that "these are my mice" and that "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 such notices were made 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 similar games to World of Warcraft. She thought that this was the only way to accomplish such a study, as epidemiologists were limited to observational and retrospective studies, because it would be unethical to release an infectious disease into the population. She added that a computer model would be insufficient as well, as it uses mathematical rules to approximate human behavior. Doctor 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. 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.

Model for terrorism research[]

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, which could provide a more realistic models for military intelligence analysts. For example, one self-confessed virtual bioterrorist in World of Warcraft commented about how quickly people got smart about doing the most damage to the largest number of people. Yale University terrorism expert Stuart Gottlieb admitted that while 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." 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.