Latest version of VirtualBox in 12.04 repositories is 4.1.* at the moment. If you want latest 4.3.* version you have to install from their repositories:
echo 'deb http://download.virtualbox.org/virtualbox/debian precise contrib' | sudo tee -a /etc/apt/sources.list.d/virtualbox.list wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add - sudo apt-get update sudo apt-get install virtualbox-4.3
