I HAVE THE ABILITY TO USE THE UPDATE OF ONE COMPUTER TO UPDATE OTHER COMPUTERS WITHOUT CONNECTING THEM TO THE INTERNET
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To Update from 4.8 to 5.0 just download new setup from http://www.avast.com/download-software#tab2 depending on your license (Free, Pro or upgrade to Internet Security).
To update virus-database download update from: http://www.avast.com/download-update
Download the update here: http://www.avast.com/download-update
Or copy 400.vps file from an updated avast installation to a USB stick and transfer it to the \Data folder of the off-line computer (having disabled the avast self-defence module first).