Installation of VirtualBox in Ubuntu 12.04

using the terminal:

1. add the virtual box key to our list of repository

wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add 

2. add the virtual box repository to our list

sudo sh -c 'echo "deb http://download.virtualbox.org/virtualbox/debian $(lsb_release -sc) contrib" >> /etc/apt/sources.list'

3. update your repository

sudo apt-get update

4. install virtual box

sudo apt-get install virtualbox-<version_number>