Atom uses PACE Anti-piracy technology to ensure licenses are distributed and activated appropriately. 

Thus to use Atom you'll need an internet connection initially to put your Atom license either onto an iLok or onto a specific computer through the iLok License Manager.
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Once the machine has an Atom license activated onto it or an iLok which holds an Atom license is inserted an internet connection is no longer required.
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The article below explains how to move your license over to a physical iLok:

​http://avid.force.com/pkb/articles/en_US/How_To/How-to-transfer-license-from-iLok-cloud-to-iLok-key?retURL=%2Fpkb%2Farticles%2Fen_US%2Fhow_to%2FHow-to-activate-license-to-the-iLok-cloud&popup=true
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