A SYN-ACK flood is an attack method that involves
sending a target server spoofed SYN-ACK packet at a high rate. Because a server
requires significant processing power to understand why it is receiving such
packets out-of-order (not in accordance with the normal SYN, SYN-ACK, ACK TCP
three-way handshake mechanism), it can become so busy handling the attack
traffic, that it cannot handle legitimate traffic and hence the attackers
achieve a denial-of-service condition.