Apple's decision has prompted an urgent hunt for an alternative way to track user behaviour in a way that is useful for developers and advertisers, but will satisfy Apple and privacy campaigners' concerns. Adfonic has outlined a number of new techniques that could be used.

The first is known as and is described as an "open source initiative for a universal and persistent UDID solution for iOS". It works by generating an identifier the first time it is requested by an application, not by taking an existing code, and then the same code is shared with any other app that requests it. However, in order to protect privacy, it can be removed or regenerated at the user's request.

"The main motivation here was to find a UDID replacement not owned by any single provider. It is easy to foresee a fragmented market where UDID management is operated by multiple providers with no cooperation between them. This open source initiative is to enable a better solution for thousands of other mobile app developers," wrote Yann Lechelle, the project's initiator and co-founder of Appsfire on the project's webpage.

But there are some solutions that are being proposed by single providers such as . Its internal research and data science department has created a "highly accurate" unique device detection system (UUD) for tracking and analysing the mobile audience.

Though Madvertise hasn't gone into the finer details of how the system works, it says that there is "a scientific method being applied to measuring, in real-time, the value of information available from a device and how much information is required in order to identify a device uniquely".