ODIN (Open Device Identification Number)

ODIN (Open Device Identification Number) is a unique identifier derived from a mobile device’s Wi-fi  media access control (MAC) address. Identifiers, which are hashed to protect user privacy, are managed by the ODIN Working Group, a consortium of industry developers and service providers.

Unlike Web pages, which use cookies to serve ads, mobile advertising requires a unique device identifier to target advertisements. Device identifiers allow marketers to provide personalization and cap ad frequency. A primary goal of the ODIN working group is to create a secure anonymous device identifier for the mobile advertising industry whose use does not intrude upon the user experience or violate the end user's privacy. 

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The ODIN working group maintains a web page.