Oooooh thats just not nice.
I believe corrupted blood is a reference to a minor bug that lead to...well, a plague, on several servers in World of Warcraft. There is a boss, Hakkar the Blood God, who has a spell, corrupted blood. Anybody he casts in on spreads it automatically to nearby people, it does some pretty nasty damage. Apparently, a hunter got corrupted blood onto his pet, dismissed it, then resummoned it inside of some area with NPCs, which spread it to all other players in the immediate vicinity, as well as the NPCs. Due to a bug, the NPCs caught and spread the effect without being killed by it themselves, thereby turning into little markers of death for anybody to wander by. I think. I only have like third-hand knowledge of the events myself.
In fact, here you go