How do online Nerve Gear games handle player authentication? So there is a virtual reality device, the Nerve Gear, popularly used for MMOs.

As far as I'm concerned, we never see SAO or Alfheim using any sort of login screen.

Now, it makes sense for SAO to lack a login screen, since you can't log out. But what about Alfheim? How do normal, sane games authenticate their players?


Do MMO Nerve Gear games use username/password credentials?

Is it implied anywhere in the series? If I recall correctly, Kirito would just put on his Nerve Gear and instantly enter Alfheim without any sort of password screen.

Maybe the device serves as the credential itself?

But if I steal your device, I could impersonate you in all games...
Besides, using a device ID is not secure at all. If I figure out your device's ID, I could hack mine to use such ID and then login as yourself.

Perhaps they do some complex biological scan on your body to create an unique ID...

That doesn't sound very reliable. Or healthy.
Your question can pretty much be answered by watching episode 1 of Sword Art Online.

The Nerve Gear uses a username and password identification system as shown at 01:37 of episode 1.



But as you mentioned, this does not occur in Alfheim Online. This is where we can consider the Nerve Gear to be the authentication factor, being a device that stores the save data.


   We know it can save data Yui's data was saved to his Nerve Gear and was transferred to Alfheim Online as a result.





  But if I steal your device, I could impersonate you in all games...


This would indeed be true, but doesn't the same count for login credentials? If you steal somebody's username and password, you can also impersonate that person in game. And don't forget, it's harder to steal physical objects all around the world than to steal some username and password from your home computer.