NonWonderDog [he/him]

At least the rumor at the time was that these things suffered from a physical “virus.”

If you ever put a damaged Zip disk in your drive, it would damage the drive (the click of death). That drive would then damage any Zip disk you put in it, spreading the virus.

To this day I don’t know if that’s actually true, but everyone believed it.

No, they have it right. Add-on software means “added to this node/machine”, as in not part of the system image used to configure multiple machines. It’s all very archaic.