Unlike Google, which crawls the Web looking for websites, Shodan navigates the Internet's back channels. It's a kind of "dark" Google, looking for the servers, webcams, printers, routers and all the other stuff that is connected to and makes up the Internet. 

Shodan runs 24/7 and collects information on about 500 million connected devices and services each month.

It's stunning what can be found with a simple search on Shodan. Countless traffic lights,security cameras, home automation devices and heating systems are connected to the Internet and easy to spot.

Shodan searchers have found control systems for a water park, a gas station, a hotel wine cooler and a crematorium. Cybersecurity researchers have even located command and control systems for nuclear power plants and a particle-accelerating cyclotron by using Shodan.

What's really noteworthy about Shodan's ability to find all of this -- and what makes Shodan so scary -- is that very few of those devices have any kind of security built into them.