I found the answer to Quora, answered the technical director of Flurry. They use different data points to bind a specific click to a specific user of the application. They claim that their accuracy is about 90%.
The data points they use include click time on installation time, device type, user location, etc.
http://www.quora.com/Flurry/How-does-Flurry-user-acquisition-work-1
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