Each Wii has a unique "Hollywood" chip key used to encrypt its NAND. A nand.bin file is useless without the matching keys.bin file from the same console .
Using shared NANDs on services like Wiimmfi can result in a console ban if anyone using that shared file is caught cheating. How to Create Your Own (Safe) NAND Backup Wii Nand Backup Files Download
The most reliable way to secure your Wii is to create your own backup using BootMii . Each Wii has a unique "Hollywood" chip key
Wii NAND Backup Files Download: A Guide to Protecting Your Console Wii Nand Backup Files Download