Is it possible to...

Is it possible to hack into someone's computer through a multiplayer online computer game such as Diablo II, or Starcraft, or Warcraft III? Because my mom won't let me play ANY of those games online because she says that when you're playing with them, you're sharing information and they can hack your computer using the game to get information to hack you. Is it possible? And if it is, is their any way for me to prevent it?