unable to download any software

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http://www.ubuntux.org – I am not able to download even a single software from Ubuntu software center,even though I am connected to network. when I used the command : sudo apt-get update && apt-get upgrade, I got the following errors: Err http://security.ubuntu.com oneiric-security InRelease Err http://security.ubuntu.com oneiric-security Release.gpg Unable to connect to security.ubuntu.com:http: [IP: 80] Err http://us.archive.ubuntu.com oneiric InRelease Err http://us.archive.ubuntu.com oneiric-updates InRelease Err http://us.archive.ubuntu.com oneiric-backports InRelease Err http://us. (Distributions)