Apple's annual developer conference in San Francisco.
Apple Sending Confirmation Emails To Combat App Purchase Fraud
MacRumors reader Michael had his iPhone replaced at an Apple Retail Store. After the first App Store purchase on the replaced phone, he received the above email. The email doesn't require confirmation of the purchase, but is instead a simple notification that a new device has been used and requests the user change their password if they don't recognize the activity.
Apple already requires credit card users to reenter the 3 or 4 digit CID number from the back of their credit card (front in the case of American Express) to authenticate the new device, however users with balances from iTunes Store Gift Cards aren't required to perform any special authentication other than entering their AppleID password.