Over 12 million unique device identifiers (UDID), and related, personally-identifiable information, for iPhones, iPod touches, and iPads have reportedly been hacked from an FBI laptop using a Java vulnerability. AntiSec has released 1 million of the UDIDs as proof of the hack, along with a statement that includes the following:
During the second week of March 2012, a Dell Vostro notebook, used by Supervisor Special Agent Christopher K. Stangl from FBI Regional Cyber Action Team and New York FBI Office Evidence Response Team was breached using the AtomicReferenceArray vulnerability on Java, during the shell session some files were downloaded from his Desktop folder one of them with the name of "NCFTA_iOS_devices_intel.csv" turned to be a list of 12,367,232 Apple iOS devices including Unique Device Identifiers (UDID), user names, name of device, type of device, Apple Push Notification Service tokens, zipcodes, cellphone numbers, addresses, etc. the personal details fields referring to people appears many times empty leaving the whole list incompleted on many parts. no other file on the same folder makes mention about this list or its purpose.
UDIDs are used by developers to register devices with Apple's iTunes Connect so they can run beta versions of iOS and test ad-hoc versions of their apps prior to release. While some developers also used to use them to identify users and their devices, Apple has now disallowed that practice.
No accounts or passwords appear to have been compromised, so for users this is more of a privacy issue than a security issue. Any single piece of identifying information, be it a UDID number or a cell phone number, when combined with a sufficiently large pool of data and the right kind of analytics, can be used to create profiles and assess patterns.
AntiSec says they released the information to draw attention to what they claim is the FBI's collection of it.
You can read more of AntiSec's statement, and find the list of disclosed UDIDs, via the link below.