Each smartphone is uniquely differentiated from hundreds of millions of other smartphones by something called an Advertiser ID. This is also known as an AAID (Android Advertiser Identification) and Apple’s is called IDFA (Identifier For Advertisers). These were implemented when IP Addresses were set to cycle every few minutes on mobile devices to protect the device users whereabouts. These ID’s are used for advertisers to track users to show them appropriate ads. This Advertising ID can only be obtained if you have a mobile application installed on a person’s phone, and you have their permission to use it.