I have contact Apple via live chat yesterday and they assist me with a healthy restore for my iPhone 5S and the explained the correct way to avoid corruption or fault during the update to iOS 8.0.2.
1. Open iTunes (Make sure is updated).
2. Plug your iPhone by the original USB cable to your laptop / PC.
3. Get back up.
4. Restore it and make sure your internet speed is acceptable and you have enough data.
5. After restoring plug off your iPhone and start it as new Phone " You will see welcome message " accept and agree.
6. Try to use all the application Safari, Siri, Camera, Make call, send SMS .. etc for 3 minutes min.
7. Plug your iPhone again and get you back up back.
This is the correct and healthy way to download iOS & Restore on your device and this what Apple technical support mentioned.