root@murtas:/etc/apt/sources.list.d# nano backports.list
root@murtas:/etc/apt/sources.list.d# apt-get update
Hit http://ftp.pt.debian.org wheezy Release.gpg
Err http://mirrors.fe.up.pt.debian.org squeeze-backports Release.gpg
  Could not resolve 'mirrors.fe.up.pt.debian.org'
Hit http://security.debian.org wheezy/updates Release.gpg
Hit http://security.debian.org wheezy/updates Release
Hit http://security.debian.org wheezy/updates/main Sources
Hit http://ftp.pt.debian.org wheezy-updates Release.gpg
Hit http://security.debian.org wheezy/updates/main amd64 Packages
Hit http://ftp.pt.debian.org wheezy Release
Hit http://ftp.pt.debian.org wheezy-updates Release
Hit http://security.debian.org wheezy/updates/main Translation-en
Hit http://ftp.pt.debian.org wheezy/main Sources
Hit http://ftp.pt.debian.org wheezy/main amd64 Packages
Hit http://ftp.pt.debian.org wheezy/main Translation-en
Hit http://ftp.pt.debian.org wheezy-updates/main Sources
Hit http://ftp.pt.debian.org wheezy-updates/main amd64 Packages/DiffIndex
Hit http://ftp.pt.debian.org wheezy-updates/main Translation-en/DiffIndex
Reading package lists... Done
W: Failed to fetch http://mirrors.fe.up.pt.debian.org/debian-backports/dists/squeeze-backports/Release.gpg  Could not resolve 'mirrors.fe.up.pt.debian.org'

W: Some index files failed to download. They have been ignored, or old ones used instead.
root@murtas:/etc/apt/sources.list.d#