Updated (DD-MM-YYYY): 01/09/2019 They are everywhere. On each OS and continent. They keep a lot of amount servers and infrastructures around the world. Usually, they are hidden from the “civilians”, but still deadly important. There are simple ones, called temporary (common scenario). But there are very advanced examples as well. Sometimes they replace normal software as it’s much simpler, but sometimes they only act as a glue. Sometimes removing only 1 tiny piece of such “unimportant” element is practically impossible, as the rest part of project/infra would fall apart.