“An online hacker group associated with Anonymous claims to have posted 1 million Apple Unique Device Identifiers (UDIDs) by breaching FBI security.
A UDID is the unique string of numbers that identifies each iOS device, formerly used by developers to track their app installations across Apple’s user base.”
Source: AntiSec claims to have snatched 12M Apple device IDs from FBI | Security & Privacy – CNET News