The epidemic began on September 13, 2005 when Blizzard Entertainment, the developer of World of Warcraft, introduced a new instance called Zul’Gurub into the game as part of patch 1.7. Inside this instance was a boss named Hakkar the Soulflayer, alluded to as the “blood god”. Players who fought Hakkar were affected by his debuff (a spell which has a negative effect over a fixed period of time). The debuff, in this case, was Corrupted Blood, a spell that caused 250–300 points of damage (compared to the average health of 2500-5000 for a player of the highest level, and with those at the mid-levels having about 1500) every few seconds to the afflicted player. The affliction was passed on to any players standing too close to infected players. While the curse would kill most lower-level players in a matter of seconds, higher-level players could keep themselves alive (via healing spells, having high stamina, or other means) long enough to spread the disease around the immense landscape inside the game. Death caused by the debuff did not cause any durability penalty, unlike most other causes of death in the game. NPCs, combat pets, and non-combat pets were key in spreading the plague.[1]

The disease would eventually go away as time passed or when the infected character died. The only way that a player was able to bring the disease outside of Zul’Gurub was by allowing a pet to get the debuff, dismissing the pet in less than five seconds, then summoning it in a populated area. (When dismissed, the pet retains the debuff and the timer of the debuff is paused.) This debuff transmission technique was first seen with the “living bomb” debuff from Baron Geddon in Molten Core.