What is the effect of the --open flag, and how does it influence the output?

• A. It increases scan speed by using parallel threads.
• B. It shows all ports including closed ones.
• C. It reveals the service versions.
• D. Prints only ports that are open, reducing noise.

Answer: (D)

The flag filters the output to show only ports that are open. In a typical scan, Nmap reports ports as open, closed, or filtered. By using this flag, you tell Nmap to display just the open ones, hiding the others. This makes the results much louder focused on reachable services, reducing noise and helping you quickly identify what you can actually access. It doesn’t change how the scan runs, nor does it reveal service versions (that requires -sV). It also isn’t about speeding up the scan or listing all ports, including closed ones—the latter would be the default behavior without the flag.