What is the effect of --top-ports 100 in an Nmap scan?

• A. Scans all ports.
• B. Scans only well-known 100 ports.
• C. Scans the most commonly used 100 ports.
• D. Disables port scanning.

Answer: (C)

This option focuses the scan on ports that are most likely to be in use. Nmap maintains a ranked list of ports by how frequently they appear in network services, based on past scans and usage data. When you set top-ports to 100, Nmap will only attempt to scan the 100 ports at the top of that list, rather than scanning a larger range of ports. This speeds up the scan and concentrates results on the ports where services are most often found. However, you might miss services that run on less common ports, since they aren’t included in the top 100. It’s not the same as scanning the entire well-known range (or all ports) and it’s not disabling port scanning—it's narrowing the scope to the most frequently used ports.