Unlike Google, which focuses on the search for web sites, Shodan is a search engine focusing on SEO elements connected to the Internet. It includes a variety of servers, peripherals,printers , and routers with IP addresses, and other sensitive information are accessible to all. It is therefore possible to use search feature patterns to retrieve lists of specific items, Honeypots and more.
Similar to Google Dorkz, a research, combining the name of an application and a version number given, and will allow anyone to retrieve the results for items with the desired version number of the application. By defining this way a version known for its vulnerabilities, an attacker will therefore be able to get a list of potentially exploitable targets through this version of the application. It is possible for example that the striker recovers all IP for the servers providing integrated command line interfaces or vulnerable versions of the SSH protocol. The same goes for the fallible versions of VNC or a set of services, such as Telnet or FTP which are not characterized by the high level of security that makes their use.
As such purpose of Shodan is purely to provide data to Security and Research professionals but it may prove dangerous if get attention by bad elements.
Find more details about Shodan from Official web pages