The Corrupted Blood Incident
4 min read

The Corrupted Blood Incident

A story of the accidental World of Warcraft pandemic.
The Corrupted Blood Incident

As we celebrate the 1-year anniversary of the COVID-19 pandemic, watching the days blur together in a haze of Zoom meetings and streaming shows, I wanted to talk about another pandemic that happened, about 16 years ago.

Most people haven’t heard of it, despite infecting over a million people over the course of a couple of weeks. That’s understandable, because this was a digital pandemic: it took place entirely within the World of Warcraft.

Hakkar the Soulflayer

Hakkar the Soulflayer

Back in 2005, Blizzard Entertainment (the company behind World of Warcraft), introduced a new raid called Zul’Gurub into the game. Raids, if you aren’t familiar, are self-contained dungeons with individual layouts and bosses. They reward players with experience, gold, and items when completed.

The final boss at the end of Zul’Gurub was Hakkar the Soulflayer. Raid bosses are, by design, difficult to kill, and Hakkar the Soulflayer was no exception. Hakkar was a blood good, sort of like a vampire on steroids. Not only did he have powerful attacks, and lots of health, but he also employed a devastating final move known as Corrupted Blood - it would drain a player’s health, and would immediately spread to any nearby players. Corrupted Blood could not be cured and could not be deflected - it was lethal to all but the most experienced players.

Now, the Blizzard developers were no amateurs. This wasn’t the first time they had created a spell like Corrupted Blood, and they knew that it would have terrible consequences outside of the raid. So they coded the game in a way that removed Corrupted Blood from any player once they left Hakkar’s dungeon. But, of course, there was something they hadn’t counted on - pets.

In World of Warcraft at the time, players had the option to keep pets, which followed you around to assist in battle. Pets could be dismissed and summoned anytime, and anywhere. As it turned out, when players dismissed their pets, the game remembered any spells that were actively affecting the pets, and when they were later summoned, the pets would reappear… with these spells still active.

I think you can see where this is going. Leaving Hakkar’s dungeon removed Corrupted Blood from any players — but not their dismissed pets. The game’s hounds, cats, and devilsaurs became unwitting vectors for this new plague.

Some of the pets in World of Warcraft


Whoever the first person to trigger this bug was (Blizzard has never released a name), they likely did so with complete obliviousness. But every time they summoned their pet outside of the raid, it would immediately infect themselves and anyone who happened to be standing close to them.

Weaker players stood no chance against the disease — they would quickly be killed, respawn, and then be killed again. NPCs were susceptible to the infection, but couldn’t die, which turned them into asymptomatic carriers. Within days, the game’s cities and towns were completely contaminated. Many players had no option but to abandon them, leaving only piles upon piles of corpses.

Looking back, it actually mimicked a real world pandemic to a surprising extent. From an article written around that time:

[The pandemic] originated in a remote, uninhabited region and was carried by travelers to urban centers; hosts were both human and animal, such as with avian flu; it was spread by close spatial contact; and there were asymptomatic individuals - in this case, invulnerable NPCs.
Blizzard attempted to institute a voluntarily quarantine to stem the disease, but it absolutely failed.  Some players didn’t take the threat seriously…
Those with healing capability volunteered their services in city centers. Lower-level characters who could not tangibly pitch in warned others away at city limits. Nervous players fled to areas known to be uninfected. Suspicion and fear was rampant over in-game communication, blogs, and email.

Of course, not everyone responded so valiantly. Many players saw Corrupted Blood as an incredible opportunity to troll others (“griefing,” as it’s called). These trolls would infect themselves with the disease, then teleport into the middle of a densely populated area, immediately infecting everyone.

A commemorative WoW server blade

Hard Reset

While there were definitely some similarities with COVID-19, Corrupted Blood was in fact a much more sinister pathogen. For one, it had a 100% infection rate. For two, there was no way to build up immunity - players would keep getting reinfected, no matter how many times they had died from the disease before. And thirdly, players could (and would) teleport instantly across cyberspace, which for better or worse is not an ability we have in meatspace.

In the end, Corrupted Blood devastated World of Warcraft’s normal gameplay. Blizzard attempted to fix the game by rolling out small patches and updates, but it wasn’t enough. After more than a week of trying and failing to contain the pandemic, Blizzard decided to pull the plug. The company did a hard reset of the affected servers, and took everything back in time to before the pandemic began.

Funnily enough, nobody was sure at first whether or not the pandemic was intentional. Blizzard had made major, impactful changes before to promote new game content, and it wasn’t outside of the realm of possibility. And in fact, they would later do just that — in 2008, they released a zombie outbreak on purpose in advance of WoW’s second expansion, Wrath of the Lich King. This time, they made sure to code a cure.

World of Warcraft: Wrath of the Lich King