The smurf and fraggle attacks are denial of service (DoS) attacks that exploit an IP prefix network and broadcast address. The smurf attack (named after the exploit program written by Tfreak in 1997) uses Internet Control Message Protocol (ICMP) echo reply packets to disable the target system. The fraggle attack (a variation of the smurf code, also written by Tfreak) uses User Datagram Protocol (UDP) echo packets directed at the Unix UDP services echo (port 7), chargen (port 19), daytime (port13) and qotd (port 17).