Remembering the Corrupted Blood incident: That time WoW was overrun by a virtual plague now referenced by Covid-19 researchers

As World of Warcraft turns 20 years old, we've been looking back at how the influential MMO changed the DNA of videogames as a whole, as well as remembering specific moments like the time adding playable dragonfolk brought a decade-old loot system to its knees. One incident stands out in terms of reaching beyond the world of videogames though, and that's the Corrupted Blood plague.

In 2005, a bug allowed a damage-over-time effect from a raid event to spread outside the confines of the boss fight it was designed for. The Corrupted Blood debuff was created to affect players as they fought Hakkar the Blood God, lowering their health and splashing from player to player if they stood too close. When it first escaped containment, nobody knew where it came from—they just logged on to find streets full of skeletons in the cities of Azeroth.

It took almost a month for Blizzard's patches and rolling restarts to halt the spread of Corrupted Blood, by which time it had infected more than four million players. Some of those infections were simple proximity contagion, but there was also an element of malice, with groups of players deliberately catching the plague and using healing magic to delay their deaths so they could spread it to cities belonging to rival factions.

At the time, it was surprising that researchers could use the Corrupted Blood incident as the basis for a paper about the untapped potential of virtual game worlds to shed light on real world pandemics. But looking back with Covid-19 fresh on our minds, it makes a lot of sense. The epidemiologists who wrote that paper eventually used it as the basis for actual Covid-19 research, as social factors in the real pandemic resembled those of the digital one. People weren't deliberately infecting themselves to grief their neighbors in real life, but early in the pandemic, Dr. Eric Lofgren saw a parallel in refusals to quarantine.

"You start to see people [say] like, 'Oh this isn't a big deal, I'm not going to change my behavior. I'm going to the concert and then going to see my elderly grandma anyway,'" said Dr. Lofgren in 2020. "Maybe don't do that. That's a big takeaway. Epidemics are a social problem... Minimizing the seriousness of something is sort of real-world griefing."

The Corrupted Blood incident was memorialized by Blizzard with its own Hearthstone card, and referenced in the Scourge invasion that took place as part of the Shadowlands expansion in 2020. Like an infection, the influence of Corrupted Blood spread beyond the place where it began, and BioWare was inspired to create the Rakghoul plague in Star Wars: The Old Republic, a zombie apocalypse that affected Tatooine. The Corrupted Blood incident has now entered the MMO hall of fame alongside historic moments like the assassination of Lord British in Ultima Online or Final Fantasy 14's catgirl army blockade, a you-had-to-be-there war story the old heads can share while noobs listen in disbelief.

We told the story of the Corrupted Blood incident in full ourselves in the documentary series Tales from the Hard Drive, hosted by Lenval Brown, the voice actor who narrated Disco Elysium. You can relive those heady days for yourself by watching it below.