How to back up multiple users using system/admin account on Windows 10? (Cryptolocker defense)

I have three ordinary user accounts on Windows 10, and one admin account. I want to back up the three ordinary users' files to an exteal drive -- but I want the backup to run as the admin. (That way, I think, if a user gets crypto-locking malware, the malware won't have write permissions on the user's backup.)

In Windows 7, I'd run Windows Backup as admin. In Windows 10, it looks like I have to log in as each user and tu on File History Backup. Which user account will that backup process run as?