vi /etc/apt/sources.list

deb http://security.debian.org/ wheezy/updates main
deb-src http://security.debian.org/ wheezy/updates main

deb http://cdn.debian.net/debian/ wheezy main contrib non-free
deb-src http://cdn.debian.net/debian/ wheezy main contrib non-free

vi /etc/apt/preferences
Package: *
Pin: release a=stable
Pin-Priority: 1001

AND:

apt-get update
apt-get upgrade
apt-get dist-upgrade