Beginning May 1, Apple will automatically reject any app updates or new applications that access Universal Device Identifiers, or UDIDs. Apple deprecated the method of tracking user statistics with iOS 5 and has been previously rejecting apps that read the UDID without user permission for at least a year, but the new deadline is seen as a hard limit that will require developers and advertisers to use other measures, such as the Vendor Identifier or Advertising Identifier introduced in iOS 6. Most apps have already changed over.
