Shodan is a public search engine that is used to locate systems accessible from the public Internet. John Matherly says the ICS-CERT alert on the ability to find SCADA systems using Shodan has received a lot of attention. He says the alert just scratches the surface of SCADA and ICS System insecurity. Shodan s creator provides suggestions for shielding these systems from the attentions of search engines, curious netizens or would-be attackers. The good news is that a few, simple security precautions would prevent the problems mentioned in the alert.
Source: https://threatpost.com/exposing-scada-systems-shodan-110910/74644/