Sep 22nd, 2016

In 2005, Blizzard unveiled a new raid called Zul’Gurub for their online role-playing game, World of Warcraft. The 20-man instance featured an end-boss called Hakkar the Soulflayer, a giant snake-like creature with several nasty debuffs, or negative effects.


One of those negative abilities was called Corrupted Blood. This ability was considered a raid killer, as it would periodically deal 200 damage every 2 seconds. During this time in the game, players usually had around 3000-5000 health, depending on their role in the party. While the health drain was bad, what made it so hard to deal with is the debuff was communicable. It could be passed along to anyone else in the raid who stood too close to an infected player.

While Corrupted Blood was an excellent way to test healers and magic dispellers in a raid, it also had some unintended consequences when it escaped the instance for which it was intended.

Spreading Disease in a Virtual World

Players soon discovered that Corrupted Blood could be manipulated outside of the instance through a clever oversight. At that time, when Hunters dismissed their pets, they kept all the buffs and debuffs that were attached to them. That meant a Hunter character could attend a Zul’Gurub raid, ensure his pet is infected, and then dismiss him immediately.

Once back inside a major city like Ironforge, Orgrimmar, or Stormwind, the infected pet could be summoned to spread the plague among the entire population of the server. And that’s exactly what happened.

Once the disease was in the open world, it began to wreak havoc. Remember that high amount of damage I mentioned? 200 damage every two seconds for ten seconds. That’s 1,000 points of damage within ten seconds. Lower level characters were wiped out immediately. There were piles upon piles of player skeletons stacking up in the cities as the disease marched its way across the population of the servers.

Blizzard tried to issue a quarantine to players who were online, some gleefully spreading their disease, others running in fear from populous areas in an attempt to escape the graveyard march. Eventually, the only way to fix the issue was to reset the servers and rewrite the code so that Corrupted Blood could not exist outside of the instance.

How this disease spread has real life applications

When news of the virtual plague began spreading outside the gaming realm, a number of real world epidemiologists took interest in the case. It’s an epidemiologists job to predict how and when disease would spread, so seeing real human reaction to a virtual disease was intriguing for scientists. They soon began publishing papers about the event.

According to them, the way users reacted to the pandemic could provide a valuable insight into how the human mind would react in a similar real-life situation. The scientists stated that researching this virtual spread of disease could lead them to better predict human behavior.

Epidemiologists rely on complex mathematical models to determine how an infectious disease could spread among a population. Because it’s highly unethical to test the validity of these models, we have to rely on information that hasn’t actually been tested. That’s why virtual plague spreading is so important.

According to one researcher, the way the Corrupted Blood plague spread is very similar to how bird flu and SARS spread in Asian countries. In the case of those real-life diseases, ducks were the carriers. Sound familiar?

Virtual plague with real, human reactions

The most interesting thing to surface from these papers is the behavior displayed by multiple people who were online at the time of the Corrupted Blood incident. Scientists noticed that some players took to protecting weaker allies, using their healing spells and shields to help them escape the pandemonium overtaking the major population centers as the disease spread.

Still, others were subject to what one researcher calls the “stupid factor.” They heard about the event online and wanted to see it for themselves, logging into an infected city and contracting the disease, only to spread it around to their allies.

Both of these types of behaviors were exhibited in real-life epidemics, too.