- Monitoring your own network or that of your clients for exposed ports
- Researching Internet topology, or performing aggregate queries like “how many nginx servers are connected to the Internet”
Can you use it maliciously? Yes. But, most of the time, if you have a target it would make more sense to do the port scan yourself. And if you’re just dragnet searching for vulnerabilities, most you find will probably already have been exploited. Sites like shodan are good for the overall health of the web because they force website owners to maintain security posture. If you know that foregoing a wordpress upgrade means you’re one script kiddy with a shodan account away from getting hacked, you’re going to keep your site up to date. This saves you from script kiddies, but also from the more sophisticated hackers who would run a port scan themselves anyway.
