They are probably mining XMR
There's a LOT of places with crypto mining softwares installed without permission, like Schools, big companies, datacenters, research facilities etc
This is not good for our crypto world, it's illegal
Almost three years ago I saw a tutorial that letting you install software that lets you mine Monero without being detected. most of the people installed their software in the internet cafe. they go one after another, just like planting a tree but in an illegal way. The owner of those internet cafes are innocense because the software that those people installed are hidden in the task manager. that's how dangerous that miner software is.
But all of those things are illegal, you are just like using people's property without their will.
It might be hidden in the task manager but you can still tell it is there. The computers will slow down a lot. Unless they were clever and only used a certain amount of the pc's power to mine so that it lasts longer without detection. If you have hardware monitoring software you can definitely figure out what's going on. I wonder how much these people actually made. I know they have botnets. I thought you might need a botnet to have enough hash power.