Explanation: Port scanning identifies open doors to a computer. Hackers and crackers use this technique to obtain unauthorized information. Port scanning is the first basic step to get the details of open ports on the target system. Port scanning is used to find a hackable server with a hole or vulnerability. A port is a medium of communication between two computers. Every service on a host is identified by a unique 16-bit number called a port. A port scanner is a piece of software designed to search a network host for open ports. This is often used by administrators to check the security of their networks and by hackers to identify running services on a host with the view to compromising it. Port scanning is used to find the open ports, so that it is possible to search exploits related to that service and application. Answer: D is incorrect. Phreaking is a process used to crack the phone system. The main aim of phreaking is to avoid paying for long- distance calls. As telephone networks have become computerized, phreaking has become closely linked with computer hacking. This is sometimes called the H/P culture (with H standing for Hacking and P standing for Phreaking). Answer: A is incorrect. It is defined as a system using a physical attribute for authenticating. Only authorized users are provided access to network or application. Answer: B is incorrect. It is described as a form of eavesdropping in which special equipments are used to pick up the telecommunication signals or data within a computer device.