A programming oversight allowed the debuff to spread beyond the website of the Hakkar boss fight and to wow classic gold the world at large. Hunter characters may summon and dismiss pets to fight at their side at will. Once ignored, all of the effects on the pets are paused until it's known as back out again. In consequence, the pets could contract Corrupted Blood during the boss fight, vanish then display the symptoms again elsewhere in the world map if they were summoned. There it would spread to other pets and players which came in contact with them.

Cities like the dwarven town Ironforge and orc town Orgrimmar were overrun in hours. Non-playable characters, who could not die due to special coding, could also catch the effect, meaning any player who passed them could get Corrupted Blood.

Once word got out, players searched frantically for news about what was going on.

"The world chat would explode any time a town fell," says Nadia Heller, an ex-World of Warcraft player whose character lived through the episode. "We kept a close eye not only on our guild conversation but on world chat as well to determine where not to proceed. We didn't want to catch it."

The spread of Corrupted Blood, and the player's behavioral changes to this, caught the interest of epidemiologist Dr. Nina Fefferman, who had been a World of Warcraft player at the time of this incident. In 2007, both published a paper that detailed their findings, such as complicated models of individual behavior in a pandemic. Fefferman claims the episode has helped inform her current research to buy wow gold classic predictive modeling around covid-19.