Port redirection is a technique by which an attacker takes network traffic coming towards a host at one port and redirects it from that host to another host. For example, tools such as Fpipe and Datapipe are port redirection tools that accept connections at any specified port and resend them to other specified ports on specified hosts. For example, the following command establishes a listener on port 25 on the test system and then redirects the connection to port 80 on the target system using the source port of 25. C.\>fpipe -l 25 -s 25 -r 80 IP_address Answer: C is incorrect. Firewalking is a technique for gathering information about a remote network protected by a firewall. This technique can be used effectively to perform information gathering attacks. In this technique, an attacker sends a crafted packet with a TTL value that is set to expire one hop past the firewall. If the firewall allows this crafted packet through, it forwards the packet to the next hop. On the next hop, the packet expires and elicits an ICMP "TTL expired in transit" message to the attacker. If the firewall does not allow the traffic, there should be no response, or an ICMP "administratively prohibited" message should be returned to the attacker. A malicious attacker can use firewalking to determine the types of ports/protocols that can bypass the firewall. To use firewalking, the attacker needs the IP address of the last known gateway before the firewall and the IP address of a host located behind the firewall. The main drawback of this technique is that if an administrator blocks ICMP packets from leaving the network, it is ineffective. Answer: A is incorrect. Snooping is an activity of observing the content that appears on a computer monitor or watching what a user is typing. Snooping also occurs by using software programs to remotely monitor activity on a computer or network device. Hackers or attackers use snooping techniques and equipment such as keyloggers to monitor keystrokes, capture passwords and login information, and to intercept e-mail and other private communications. Sometimes, organizations also snoop their employees legitimately to monitor their use of organizations' computers and track Internet usage. Answer: B is incorrect. In UDP port scanning, a UDP packet is sent to each port of the target system. If the remote port is closed, the server replies that the remote port is unreachable. If the remote Port is open, no such error is generated. Many firewalls block the TCP port scanning, at that time the UDP port scanning may be useful. Certain IDS and firewalls can detect UDP port scanning easily.