This script/program is created by Code Mobile. Iam not taking thecredit of the original author. :)

/*

My advice is to disable the echo service completely. It is often used by hackers to hang a computer.

Try sending a packet from port 7 your ip to port 7 your ip.

The system will bounce the packet back and forth slowing the system
drastically.

A Hacker Program I have seen used to do this is called codeudp.c

*/

/************************************************************************/
/* codeudp.c version 0.01 by CodeMobile - codemobile@yahoo.com */
/* Sends a single udp datagram with the source/destination address/port */
/* set to whatever you want. Unfortunately Linux 1.2 and SunOS 4.1 */
/* don't seem to have the IP_HDRINCL option, so the source address will */
/* be set to the real address. It does however work ok on SunOS 5.4. */
/* Should compile fine with just an ANSI compiler (such as gcc) under */
/* Linux and SunOS 4.1, but with SunOS 5.4 you have to specify extra */
/* libraries on the command line: */
/* /usr/ucb/cc -o codeudp codeudp001.c -lsocket -lnsl */
/* I'll state the obvious - this needs to be run as root! Do not use */
/* this program unless you know what you are doing, as it is possible */
/* that you could confuse parts of your network / internet. */
/* (c) 2011 Code Mobile - I accept no responsiblity for anything this does. */
/************************************************************************/
/* I used the source of traceroute as an example while writing this. */
/* Many thanks to Anu (pctipsbyanu@yahoo.com) and Inspired  */
/* for pointing me in the right direction. */
/************************************************************************/

#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in_systm.h>
#include<netinet/in.h>
#include<netinet/ip.h>
#include<netinet/udp.h>
#include<errno.h>
#include<string.h>
#include<stdlib.h>
#include<netdb.h>
#include<arpa/inet.h>
#include<stdio.h>

struct sockaddr sa;

....To take advantage you must DOWNLOAD FULL CODE.

Compile and execute as root 

All credit goes to  Code Mobile.

Thanks....