Which of the following tools or methods can be used to discover services running on computers?

A. HTTP interceptor
B. ping sweep
C. port scanner
D. black box

C
Explanation: Open ports indicate services that may be running and listening on a device that may be susceptible to an attack. A port scanner basically pings every address and port number combination and keeps track of which ports are open on each device as the pings are answered by open ports with listening services and not answered by closed ports.