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Legacy Prefixes

Ad-ID will withdraw all ISCI prefixes that have not been activated on the Ad-ID system as of May 15, 2018, and make them available to other advertisers to license.

The ISCI Commercial System was a database of prefixes, consisting of 2, 3 or 4 letters that identified advertisers. ISCI was replaced by the Ad-ID system in 2008. Prefixes that were licensed through ISCI are referred to as “legacy” prefixes. ISCI/legacy prefixes are considered inactive until they are activated on the current Ad-ID system. All Ad-ID codes begin with a 4-character prefix.

The list of legacy prefixes that have not been activated on Ad-ID can be viewed below.

If a company would like to use their legacy prefix, the prefix will need to be activated on Ad-ID prior to May 15, 2018. There is no cost to activate the prefix on Ad-ID. If a company does not wish to activate their assigned legacy prefix, a new 4-character prefix can be activated on Ad-ID in the future, free of charge. 

For more information on how to activate the legacy prefix, please contact the Ad-ID customer service team at (704) 501-4410 or

Download the Legacy Prefix List - Sorted by Advertiser (March 15, 2018)