Mostly used in team based on-line games, where a number of poor players are so bad, they start to effect the more skilled members of the team. Most likely becuase they are annoyed at their useless team-mates, and are too preoccupied yelling at them to concentrate on the game, or they know they have no chance of winning and just give up. Thus the cancer of a handful of useless noobs
, spreads to the whole team, making them all useless.
"IDIOT! Look what you made me do! Just go away! Give your noob cancer to some other server!"