Well that was surprising. And a little alarming.
I got a new multifunction printer, a Canon MG7120. It is connected wirelessly to my home local area network. I installed the latest drivers from the Canon website. I scanned some pages using the scan operation on the printer and selected my laptop and my username on the laptop as where to put the scans. I expected to be asked for a sign-in or something to get access to the laptop.
I got nothing, and the operation seemed to complete. My laptop was in the other room, and when I looked at it, the scans (in a PDF) had been deposited into my Pictures folder, and a new Finder window had been opened with scan PDF file highlighted!
How did the printer do that? Does the printer driver have a back door that lets the printer write into my user account? Or did I create some other sort of back door when I installed the drivers? Or did I open the door myself somehow? Is this a security hole?
I am using a relatively new Time Capsule (the taller than wide version) to create my local network, and the laptop is a 2012 MacBook Air.