Shodan is a search engine for [[Internet]]-connected devices. It is a private tool that is mostly used by cyber professionals, researchers, law enforcement etc.
It tends not to be used by [[attacker]]s, because they're generally smart enough not to pay for functionality that could be replicated with a [[botnet]].
Here's a fun video from [[DEFCON]] about all the stupid things that people leave unsecured on the Internet: https://www.youtube.com/watch?v=-T-3buBwMEQ