The more common of these are when the company gets hacked, if they have lax security and bad methods of password storage. It doesn't matter then how complex your password is. I also remember when adobe flash had a problem that allowed it to put keyloggers on, so there were adds on WoW sites that made you vulnerable. It lasted for like a week before being fixed. So besides being careful, there are still ways to get your account hacked that you can't do much about.