Disable Guest Session in Ubuntu 12.04 & 12.10

In a fresh Ubuntu installation, one of the first things need to do is to disable the Guest account on log-in screen for security. Now the popular Ubuntu configuring tool Ubuntu-Tweak has the option to turn on/off Guest account since version 0.7.3.

Here we go:
1. Download .deb package of Ubuntu Tweak from right side-bar at:

launchpad.net/ubuntu-tweak
2. Double-click to install the .deb package. But I recommend to use this 2 commands (Hit Ctrl+Alt+T to launch terminal and run command in it):
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Source: http://handytutorial.com