Install VirtualBox 4.3 on Ubuntu 14.04 from repository source

This post show how to install VirtualBox 4.3 on Ubuntu 14.04, from repository.

The list of repository sources can be found at https://www.virtualbox.org/wiki/Linux_Downloads. For 14.04 ("Trusty Tahr"), it is "deb http://download.virtualbox.org/virtualbox/debian trusty contrib".

Run the command to add apt repository to your sources list:
$ sudo add-apt-repository "deb http://download.virtualbox.org/virtualbox/debian trusty contrib"

Before update apt source list, you have to add Oracle public key. Download the Oracle public key for apt-secure (oracle_vbox.asc) from the same page. It should be like this.

Then run the command:
$ sudo apt-key add oracle_vbox.asc

Update apt-get and install VirtualBox 4.3:
$ sudo apt-get update
$ sudo apt-get install virtualbox-4.3