People build botnets by enticing people to install trojans on their computers, e.g. a free utility app or game. They can then earn money from people who want t

People build botnets by enticing people to install trojans on their computers, e.g. a free utility app or game. They can then earn money from people who want to rent access to these botnets. There are also free VPN services who, in their fine print, say that users grant them permission to route other traffic via their connections.