deb http://security.debian.org/ stable/updates main contrib
deb-src http://security.debian.org/ stable/updates main contrib
+# backports:
+ deb http://backports.debian.org/debian-backports squeeze-backports main
+ deb-src http://backports.debian.org/debian-backports squeeze-backports main
+
# official debian repository:
# deb http://ftp.debian.org/debian/ stable main contrib non-free
# deb-src http://ftp.debian.org/debian/ stable main contrib non-free