(ISC)2 Blog: Do you know Shodan?.
So here’s the basic: SHODAN (Sentient Hyper-Optimized Data Access Network) is a search engine, but instead of indexing web page content, it indexes banners information. It indexes data on HTTP, SSH, FTP, TELNET and SNMP services for almost the whole Internet. You can find it at http://www.shodanhq.com.
In other words it’s a massive port scanner to help you find vulnerable network devices. Why waste time doing your own scanning, when all you have to do is query Shodan.
