I regularly infect other peoples Laptops, and my own VMs as well, with a very common Spyware/Adware/Trojan. It comes in two different versions, the newer one being much more aggressive than the older one. It's a 'premium' product costing up to $250 officially. The only way to really get rid of it is a full disk clean, otherwise it hides itself into separate, hidden partitions. It IS very annoying to install, considering it's very slow, buggy and needs a terminal to circumvent the online account (even more tracking, technically, but I don't want to create an account myself). And it even crashes all the time, takes ages to update and is a magnet for other viruses. I myself of course don't have it, i use Linux after all. But most people seem to like Windows, for some reason, so I have to install it for them.
Well, why what? Why do I have to install it? Because there are A LOT of old people in my village, who only ever used windows, and when I repair their stuff or get them new stuff I often have to (re)install windows. And windows is the virus I'm talking about, because IMHO, it literally IS Spyware, Adware and a Trojan. Literally every criteria is met for those kinds of viruses. MacOS is just a lighter Spyware and potentially a Trojan, but can be expanded to be all three (especially a RAT Trojan) very easily. Linux, on the other hand, has only very few, single instances of separate Distros having ads (Canonical/Ubuntu) or Spyware via Telemetry (Also Ubuntu), but not only can Telemetry be disabled, one could also use another distro. Like Arch btw.