Infinity Ward has removed the Giant Infection playlist from Modern Warfare, for being too generous with XP. They say they’re working on a fix now.
The Giant— Infinity Ward (@InfinityWard) February
Infection playlist was giving out a little too much XP, so we just
rolled out a playlist update to remove the mode while we work on a
Giant Infection was added in the most recent content update, along with a new map, the addition of Shoot House to another playlist, and a range of general fixes. The mode was a version of Infected played on the Ground War maps (thanks, VG247.) It appears to have been a little glitched; it was only added a few days ago, but players have already managed to get an exorbitant amount of XP from the mode. One player even claimed on Reddit that almost 50 people managed to get over 80k XP in various games, with others saying you could just hide during the games and still progress through several levels.
Infinity Ward hasn’t clarified when Giant Infection will come back, but we’ll keep you posted.