You seem to use an older version of VirtualBox ... instead use the current version VirtualBox 5.0 :
Uninstall the old version of VirtualBox
sudo apt-get purge "^virtualbox-.*"
Remove leftovers in case there are any
sudo apt-get autoremove
Download and register the ORACLE public key
wget -q -O - https://www.virtualbox.org/download/oracle_vbox.asc | sudo apt-key add -
Add the ORACLE VirtualBox repository to the software sources
echo "deb http://download.virtualbox.org/virtualbox/debian trusty contrib" | sudo tee /etc/apt/sources.list.d/oracle-vbox.list
Update the software repositories
sudo apt-get update
Install VirtualBox 5.0
sudo apt-get install dkms virtualbox-5.0
Download the Oracle VM VirtualBox Extension Pack.
Open VirtualBox Preferences and add the extension pack.
It is recommended to restart the operating system afterwards.
Note for other users reading this answer, in case they use another Ubuntu edition as 14.04 :
You have to replace trusty
with the Ubuntu edition you are using when adding the repository !
As of Ubuntu 16.04 the ORACLE public key to download and register has changed :
oracle_vbox.asc
has to be replaced with oracle_vbox_2016.asc
!