It's not that you are infected with a virus, but that you are downloading something to establish contact with others, copying something from their computers, or that your computer has resources that others need. First of all, many people are connected to your computer to copy. You need to establish a connection if you download it. Now we can download quickly, because we don't copy things on the server, but as long as the online computer has resources, we can establish a connection with it to download.
A movie can be divided into 100 clips, and different clips can be downloaded from 100 computers at the same time, and finally a complete movie is made without combination. It is a P2P technology. If the landlord is interested, you can Baidu it.