Once upon a time, the Corrupted Blood Incident was a deadly plague that swept through Azeroth. It all began on September 13, 2005... Update 1.7 Rise of the Blood God, which featured a new raid named Zul'Gurub, was released that day. Hakkar, the Soulflayer was his final boss and he had Corrupted blood. The spell was meant to infect Hakkar's enemies, deal damage over time, and also transfer to nearby characters. The curse will only work in the raid area and should last for a few seconds. A bug in the game code was discovered and the plague was able to escape from Zul'Gurub.

Hakkar, the Soulflayer

The spell was intended for characters at the highest level. Low level players were falling like flies. NPCs spread the disease, although they didn't actually die, but were carriers so that they could pass it on. Popular locations suddenly became abandoned. Cities once brimming with life became skeleton-strewn wasteland. Although characters who die in World of Warcraft may be brought back to life quickly after death, players are still at risk of financial loss, virtual financial losses.

Blizzard attempted to fix the bug with a hotfix. Then they tried to convince players to temporarily quarantine. They decided to shut down all servers and fix the bug by making changes to the code.

The case was so serious, that both epidemiologists and antiterrorist services became fascinated in it. Scientists studied the reactions of people to the raging epidemic. Although the spell was not well-designed, scientists studied how people reacted to the raging plague. However, malicious players intentionally spread the spell in cities to prevent an epidemic. The Tainted Blood could only be spread beyond the raid walls if it infected the hunter's animal first. The infected pet could then be allowed to enter a city and infect others. It was discovered that running away and isolation were the most common reactions to the prevailing illness. Some players had healing skills and tried to help the infected. Others did it for financial gain. A group of people visited infected areas to observe abandoned cities and out of curiosity.

The Tainted Blood Incident is still the largest virtual outbreak in history. World of Warcraft was just ten months old at the time, but it had already attracted four million players. This unplanned experiment gave scientists a lot to study, and they were able to test the behavior of modern society when faced with a pandemic.