Re: "Try finding a virus that would both be capable of infecting a PDP-11"
Canada's nuclear plants will run code specificallly assembled for PDP-11 minicomputers for at least another 30 years. Try finding antivirus software for that! Or security auditors who truly understand its innards.
Good. Security by obscurity. I approve.
Look, I doubt that any young hacker would want to go thru the effort learn the PDP-11 hardware (it's HW, not an OS) architecture when there are easier targets running Windows.
And there are plenty of experienced PDP-11 engineers out there. Now that their kids have graduated and left the house, they would truly enjoy the opportunity to work on it again. Although I suggest Canada upgrade to VAX/VMS.