How to Install Oracle VirtualBox 4.3.28 on Ubuntu 15.04, 14.04, 12.04 and Debian 7/6 Linux 

Oracle VirtualBox 4.3.28 has been released on May 13th, 2015. Oracle VirtualBox 4.3.28 is a maintenance release of VirtualBox 4.3 which improves stability and fixes regression. See the ChangeLog for more details.
This article will help you to install Oracle VirtualBox on your Ubuntu 15.04, 14.10, 14.04 LTS, 13.10, 13.04, 12.10, 12.04 LTS and 10.04 LTS and Debian 7/6 systems.

Step 1: Setup Apt Repository

Firstly edit /etc/apt/sources.list file and add one of following line according to your distribution to your system.

For Ubuntu 15.04 ("Vivid")
deb http://download.virtualbox.org/virtualbox/debian vivid contrib

For Ubuntu 14.10 ("Utopic Unicorn")
deb http://download.virtualbox.org/virtualbox/debian utopic contrib

For Ubuntu 14.04 LTS ("Trusty Tahr")
deb http://download.virtualbox.org/virtualbox/debian trusty contrib

For Ubuntu 12.04 LTS ("Precise Pangolin")
deb http://download.virtualbox.org/virtualbox/debian precise contrib

For Debian 7.0 ("Wheezy")
deb http://download.virtualbox.org/virtualbox/debian wheezy contrib

For Debian 6.0 ("Squeeze") 
deb http://download.virtualbox.org/virtualbox/debian squeeze contrib non-free

Step 2: Setup Oracle public key

After adding required apt repository in your system, download and import the Oracle public key for apt-secure using following commands.

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

Step 3: Install Oracle VirtualBox

After completing above steps, lets install VirtualBox using following commands. If you have already installed any older version of VirtualBox, Below command will update it automatically.

$ sudo apt-get update
$ sudo apt-get install virtualbox-4.3

Step 4: Start VirtualBox

We can use dashboard shortcuts to start VirtualBox or simply run following command from terminal.

$ virtualbo