Final answer:
An XMAS tree scan is a technique used in computer networking to identify open ports on a target system.
Step-by-step explanation:
An XMAS tree scan is a technique used in computer networking to identify open ports on a target system.
When a network scanner sends a packet with all the possible TCP flag options set to the target system, it is called an XMAS tree scan.
The purpose of an XMAS tree scan is to elicit a response from the target system and determine which ports are open and vulnerable to attack.
The TCP flags that are set in an XMAS tree scan include the FIN (finish), PSH (push), URG (urgent), and the RST (reset) flags. The TCP flags that are not set in an XMAS tree scan are the SYN (synchronize) and the ACK (acknowledge) flags.
Therefore, the correct answer is the *SYN flag* is not set in an XMAS tree scan.