Blizzard is planning to introduce a new security measure for its MMOs, and it could be a USB dongle, if you go by the survey emails that Blizzard has sent out to the World of Warcraft subscribers.
There are many questions that point out to account security. And there is a chance they could also use a system where the passwords are changed regularly. As for the security dongle, these are mainly used by game developers when they send out the beta code to preview. The game only plays if you plug the USB dongle to the USB port.
Blizzard normally bans users if they are found to use third-party programs or bots. There is no official word from Blizzard though, but it could be a positive move from the developer and it will protect most of the gamers from trojans and keyloggers.