Howtogeek shows you how to disable Ubuntu's Guest Session Account

Ubuntu and Linux Mint come with a ?Guest Session? account, which anyone can log into from the login screen ? no password required. If you?d rather restrict access to your computer, you can disable the guest account. This guest account is locked down and changes to it don?t persist between sessions ? everyone that logs in gets a fresh desktop. Still, you may want to disable it to prevent other people from using your computer.

  How to Disable Ubuntu's Guest Session Account