[ubuntu] Disable automatic login to "ubuntu" account

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http://ubuntuforums.org – Hello, I have a liveUSB with ubuntu 11.10 on it. I have there my own account "Han" with a password, and there's also a basic account called "ubuntu". I have set a password there too, by some passwd command in terminal. The problem is, when I boot up the computer, It automatically logs in ubuntu account, without asking for password. When I Log Off, there are two options, Han & Other. When I choose Other, there username "ubuntu" and password, it logs in. The question is, how do I disable that automatic login? (Hardware)