Skype has stopped supporting older version than 4.3 due to the new security implementations. This has forced many Ubuntu users to upgrade the Skype version to at least 4.3.
To install Skype 4.3 on Ubuntu Desktop 10.04/12.04/12.10/13.10/14.04:
1) Remove older version of skype
sudo apt-get remove skype skype-bin
2) Download the package from official skype link here.
3) Install the package
sudo dpkg -i skype-ubuntu*.deb; sudo apt-get -f install
The Canonical repository has included Skype 4.3 now. Enable Canonical repository from Ubuntu software center and install skype without download the package.
apt-get install skype