The Corrupted Blood Incident

Posted by on February 3rd, 2011
On September 13th, 2005, an update to Blizzard’s World of Warcraft online game introducing the Zul’Gurub dungeon helped unleash a series of events that led to a catastrophic plague that spread out of control. In a fascinating example of cascading failures in a complex system, all hell broke loose. For an entire week the Blizzard team fought to end the plague and restore order.  As one witness to the event stated:

“There are three things you can do: infect people, die, and watch other people do the first two. There’s no way to rush for a cure; there’s no way to stop the plagued idiots from coming in, there’s no quest, no change, no nothing.”

The case has been made that games like World of Warcraft are complex systems because they share the following attributes:  “they consist of a large number of interacting agents, they exhibit emergence; that is, a self organizing collective difficult to anticipate from the knowledge of the agents behavior, and their emergent behavior does not result from the existence of a central controller.” Such complex systems require careful testing and strong controls.  An independent security consultant who played World of Warcraft at the time noted:

“Giving it the ability to propagate at all beyond a limited environment definitely reminds us that self-propagating code is likely to bite us in the ass without careful consideration and planning.”

As the plague spread from the dungeon across the world on as many as three different servers, the players panicked and the game became unplayable in its normal fashion. Cities became death traps and eventually abandoned as players either stopped playing or hid in the wilderness. In an interesting parallel to real world plagues the Corrupted Blood plague exhibited the following traits:

“it 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.”

Here is a video taken during the height of the plague.

Cascading Failures: What Happened?

The end boss of Zul’Gurub was Hakkar the Soulflayer, Blood God of the Gurubashi trolls, and if he was attacked the players received a gift called Corrupted Blood, which is basically a curse that steals health and is highly transmittable from one player to another. It was originally designed to only affect the players while they were still within the dungeon, but a combination of bugs introduced into the system and player actions combined to set the plague loose into the world. The damage done by Corrupted Blood was so massive that it killed most lower level characters instantly, but allowed more powerful characters enough time to keep moving and spread the disease even further. Corrupted Blood was designed as a short-term annoyance for very high level players and was never meant or imagined to exist outside the specific dungeon for which it was created. A series of small failures combined and cascaded to become a world event.

  1. Players had at least two ways of transferring Corrupted Blood beyond the walls of Zul’Gurub. The first way was to simply teleport from the dungeon back to a populated area. Secondly, it was possible for in-game pets to get the disease as well, but they would not lose it when they left the dungeon.
  2. Corrupted Blood also exhibited asymptomatic characteristics as the game controlled characters were not affected by the plague, but they could be carriers of it. All of the non player characters (NPC) essentially acted very much like a World of Warcraft Typhoid Mary.
  3. Players, much like humans in real life, ignored the authorities. A voluntary quarantine was issued by Blizzard, but it was ignored by many players or simply not take seriously.
  4. The final factor that played heavily into the plague was the fact that many players willfully and intentionally operated to spread Corrupted Blood throughout the lands. These players have been called the terrorists of World of Warcraft by Robert Lemos of Security Focus.

    “For a week, the efforts of malicious players left behind massive casualties, made cities nearly uninhabitable, and became a reminder of the uncontrollability of self-propagating code.”

These four basic issues combined together to create a scenario that quickly became an out of control plague. In the end, Blizzard forced a hard reset of the servers and rolled a new version of code out that addressed issues 1 and 2 listed above. Unfortunately, issues 3 and 4 are outside the ability to be repaired and will probably show up again in the future.  In more recent years, the incident has been used several times in epidemiological studies and it has even been used as a model for exploring how terrorist cells form and operate.

[Wikipedia // Corrupted Blood incident]
[WOWWiki // Corrupted Blood]
[Security Focus]
[Complex Systems Theory, Virtual Worlds & MMORPG’s: Complexities Embodied]

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