Typical Debian 7 /etc/apt/sources.list
sudo vi /etc/apt/sources.list update/add deb http://cdn.debian.net/debian/ wheezy main deb-src http://cdn.debian.net/debian/ wheezy main deb http://security.debian.org/ wheezy/updates main deb-src http://security.debian.org/ wheezy/updates main # wheezy-updates, previously known as ‘volatile’ deb http://cdn.debian.net/debian/ wheezy-updates main deb-src http://cdn.debian.net/debian/ wheezy-updates main deb http://download.virtualbox.org/virtualbox/debian wheezy contrib deb-src http://download.virtualbox.org/virtualbox/debian wheezy contrib deb http://http.debian.net/debian/ wheezy-backports main contrib deb-src http://http.debian.net/debian/ wheezy-backports main contrib