Perish the thought that the UK would ever go down the inefficient USAF route - as you well know, D-IFF_ident (it was you who told me!), they'll use 3 tankers where the RAF would only need 1!
USB nerd-paranoia apart, the mission file can also be loaded from the laptop to the on-board system by Ethernet cable.
USB pen drives used with the system are never to be used for other purposes - and the planning laptops aren't Internet enabled.
Anyway, if the system became corrupted, the crew still has a 'paper plan' they can use.