World of Warcraft screenshot showing piles of player skeletons scattered across a city from the Corrupted Blood incident

Corrupted Blood Incident

2005eventclassic

Published August 17, 2026

The Corrupted Blood Incident was an accidental virtual plague inside World of Warcraft during September 2005, when a raid boss debuff meant for one dungeon leaked out into the wider game and killed thousands of low level characters over roughly a week. The outbreak later became a serious case study for epidemiologists modeling how real people behave during pandemics.

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Overview

The Corrupted Blood Incident was an unintentional in-game plague that swept through Blizzard's MMORPG World of Warcraft starting September 13th, 20052. A boss mechanic that was supposed to stay inside one raid dungeon escaped into the game's crowded capital cities, killed weaker player characters within seconds, and forced Blizzard to fight the outbreak with hotfixes and server resets over roughly a week1. Scientists later took the whole thing seriously as a natural experiment for how real people behave during an epidemic3.

Origin & Background

Platform
World of Warcraft / Reddit (viral spread)
Creator
Blizzard Entertainment
Date
2005

On September 13th, 2005, patch 1.7 added the Zul'Gurub raid to World of Warcraft, whose final boss Hakkar the Soulflayer cast a health draining debuff called Corrupted Blood on nearby players1. Hunter class players quickly discovered they could soak the debuff on their pet, dismiss the animal, then re-summon the infected pet after fast traveling to hub cities like Ironforge and Orgrimmar, which broke the game's containment logic and seeded the plague across the wider server population3.

How It Spread

Low level characters often died in a single tick while high level players survived long enough to keep spreading the debuff as unwitting carriers1. Blizzard first asked for a voluntary quarantine, but it broke down within hours as griefers sprinted infected pets straight into busy trade districts on purpose3. Rushed patches and server resets ended the outbreak about a week after it started, and in October 2008 Blizzard nodded back to the incident with a scripted zombie infection event ahead of the Wrath of the Lich King launch1.

On May 20th, 2008, Gamasutra ran a piece titled "The Real Life Lessons Of WoW's Corrupted Blood," reporting that epidemiologist Nina Fefferman used the incident as data on human behavior during an epidemic1. On February 26th, 2011, YouTuber Christiaan008 posted a lecture called "Modelling Infectious Diseases in Virtual Realities" walking through the Corrupted Blood case4. The story kept surfacing on Reddit years after Blizzard patched the exploit, most visibly when a Wikipedia writeup on the incident was shared to r/gaming for the eleventh anniversary in September 20162.

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