How to disable guest session in Ubuntu 11.10

In your terminal write:

sudo nano /etc/lightdm/lightdm.conf

Than all you need to do is to find the section:

[SeatDefaults]
greeter-session=unity-greeter
user-session=ubuntu 

And then add:

allow-guest=false

Done deal! If you wanna allow the account again just delete the line you added in the same file. Easy peasy!