Probably would be better to use a vendor-specific salt, so you can compare users between your application. Since the UDID is just SHA1(SerialNumber + IMEI + Wi

Probably would be better to use a vendor-specific salt, so you can compare users between your application. Since the UDID is just SHA1(SerialNumber + IMEI + WiFiAddress + BluetoothAddress), adding in a "vendor ID" at the end when generating it was a huge mistake in the original iPhone SDK, and they can't fix it now.