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!"
The sickness that you get when a noob is so freakin noobie that you want to kill yourself, but you cant because you know you have to get to lvl 80!
OMG! Shut up noob, you're giving me a case of Noob Cancer.