问题
As we know Apple is deprecating developers' access to UDID. But to my knowledge it is possible to get an iDevice's MAC address. So what's the difference then? Both MAC address and UDID are unique identifier of a hardware, which is not app specific.
回答1:
Some obvious differences between UDID's and MAC addresses:
It's conceivable that a device might have more than one MAC address.
Guaranteeing uniqueness for MAC addresses isn't Apple's responsibility.
UDID's and MAC differ in size and format.
I think it's best to consider the deprecation of the UDID as Apple's way of encouraging developers to switch to other means of identification. For example, keep track of the user rather than the device by setting up a userid/password system. Tracking the UDID brings some problems, like what to do if the user loses or sells his or her device.
回答2:
Apple did in fact, deprecate UDID due to third party companies which exist for the purpose of aggregating (as in paying for) data from app developers to sell ads.
See tracking cookies, same concept. So while technically sound, and a huge convenience for developers who dont want to require a user name and password to their applications, due to third party tracking companies this ends up being disastrous for user privacy.
Apple now supports a UUID (universally unique ID) which can be genned from the SDK, which will uniquely identify that user to the application itself but not across applications.
This sandboxes the ID, doesnt require the developer to resort to hacks like MAC address, and protects the user from third party tracking schemes.
If you dont use UUID, expect Apple to reject your app. Even if you use Mac address you will not necessaliry escape detection since there is almost no reason an app would require such information to operate.
来源：https://stackoverflow.com/questions/9743880/ios-udid-deprecated-mac-address