Quoting Debian Wheezy release notes:
Some packages from proposed-updates may also be made available via the wheezy-updates mechanism. This path will be used for updates which many users may wish to install on their systems before the next point release is made, such as updates to virus scanners and timezone data. All packages from wheezy-updates will be included in point releases.
In order to use packages from wheezy-updates, you can add an entry to your sources.list:
deb http://mirrors.kernel.org/debian wheezy-updates main contrib deb-src http://mirrors.kernel.org/debian wheezy-updates main contrib
The next time you run apt-get update, the system will become aware of the packages in the wheezy-updates section and will consider them when looking for packages to upgrade.
Note that if APT::Default-Release is set in your /etc/apt/apt.conf (or in any of /etc/apt/apt.conf.d/*), then, in order for automatic upgrades to work, it is necessary to add the following configuration block into /etc/apt/preferences (see apt_preferences(5) for more information):
Package: * Pin: release o=Debian,n=wheezy-updates Pin-Priority: 990
When a new package is made available via wheezy-updates, this will be announced on the debian-stable-announce mailing list.