^
The bit about "Corrupted Blood" debuff in WoW is a little wrong.
Players did not "remain" infected to bring the plague outside of the instance (dungeon).
However, a hunter's (a class played in the game) animal pets could.
Normally the debuff goes away quickly, but some players have figured out to dismiss (temporary tuck away their pets from the game) the pet as soon as it contracted the disease, then move to a heavily populated city, and call the pet back. The pet will come back WITH the plague intact, then all the NPC (non-player characters, vendors, etc) as well as players nearby contracted the disease.
Although not instantly life threatening to higher level players, the powerful disease could kill any lower level players instantly, and since even the bank cashiers and roaming guards of the city could contract the disease, the cities quickly turned into a death-ridden corpse-lying-everywhere chaotic mess. It rendered the game impossible to play for anyone not high level, until Bilzzard patched the game so the pets could no longer be contaminated by the disease.
