Encrypt Windows 8 file history
Solution 1:
You can even use BitLocker to encrypt the drive where you make the backup and access that drive from your computer, so that File History does its job regularly.
Solution 2:
If the external drive you are backing up to is NTFS you could use EFS, by right-clicking on as file choosing properties and then advanced, and set it to encrypted. Fat32 and other formats do not support EFS but you could use something like Truecrypt.