Copy nand.bin and keys.bin from the SD card to a secure folder on your PC.
To safely back up your Wii, you need a console with the installed and an SD card (preferably 2GB or larger). Wii Nand Backup Download
The progress bar moves slowly. When it finishes, BootMii will verify the backup (another 10 minutes). Copy nand
Now that you have your own safe backup, you can use it for legitimate purposes. When it finishes, BootMii will verify the backup
Once the process finishes, take your SD card to a computer. Open the root directory of the card, and you will find two newly generated files:
This method allows you to rebuild your system from scratch without relying on anyone else's potentially dangerous data.
and don't have a backup, I can explain the "Blue-Bomb" or "SaveMii" recovery methods. Would you like to know more about Wii recovery setting up a USB loader for your games? BootMii Backup | Wii Hacks Guide