Botnets are used by hackers to take control of most any machine or device that is capable of running the bot’s code
These days, hackers don’t just focus on infecting computers or cell phones, they also tend to infect a lot of other devices that belong to the IoT domain (Internet of Things). There are cases where smart ovens are hacked and used as bots. (aw lawdy, hide your patties)
Lots of smart appliances run on Android and are not often updated with security patches, and this can present a huge issue because they are connected to the network. Same deal w/ routers, the ISP’s just don’t apply the patches and so they are left with these massive, well known vulnerabilities
Usually, infected devices which have been made into bots are used to perform DDoS attacks to bring down sites or services