User Datagram Protocol (UDP) is an unreliable packet. This means the sender of the data does not care if the receiver has received it. In UDP flooding, many UDP packets are sent to the victim at random ports. When the victim gets a packet on a port, it looks out for an application that is listening to that port. When it does not find the packet, it replies back with an Internet Control Message Protocol (ICMP) packet. ICMP packets are used to send error messages. When a lot of UDP packets are received, the victim consumes a lot of resources in replying back with ICMP packets. This can prevent the victim from responding to legitimate requests.