VirtualBox 4.3.18 for Linux (Ubuntu 14.04 LTS)

In Ubuntu 14.04 LTS, you can install VirtualBox easily from the Ubuntu Software Centre. The available version is 4.3.10. Unfortunately I was unable to install in Dell Latitude E6400 laptop. It complained:

 'VT-x is disabled in the BIOS. (VERR_VMX_MSR_VMXON_DISABLED).'

Instead of trying to fix this issue, I simply decided to install the most recent version of VirtualBox which is 4.3.18.

To install:
For my distribution, I added the following lines to my /etc/apt/sources.list:

deb http://download.virtualbox.org/virtualbox/debian trusty contrib

Then, download, add and register the Oracle public key for apt-secure using following command:

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

To install VirtualBox, do

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

For more detailed official installation instruction, please follow this link. On the page, Ubuntu/Debian users are recommended to install the dkms package to ensure that the VirtualBox host kernel modules (vboxdrv, vboxnetflt and vboxnetadp) are properly updated if the linux kernel version changes during the next apt-get upgrade. For Debian it is available in Lenny backports and in the normal repository for Squeeze and later. The dkms package can be installed through the Synaptic Package manager or through the following command:

sudo apt-get install dkms