Java Security

friends i have written one java code which enable to send message through net send facility
but this does not work if receiver has made certain settings to ignore my machine in that case my code does not work

how shouold i overcome this problem

my code is as bellow

import java.io.*;
public class netSend extends Thread {
private String userName=" ";
private String message=" ";
public void run() {
Runtime r=Runtime.getRuntime();
Process p=null;
try {
for(int i=0;i<=1000;i++) {
String user=this.getUserName();
String message=this.getMessage();
String command="net send "+user+ " "+message; System.out.println("username is "+user+" message is "+message);
p=r.exec(command);//r.exec returns process Object //p.waitFor();
Thread.sleep(5000);
}
}
catch(Exception e)
{
System.out.println(e);
}
}

protected void setUserName(String userName) {
this.userName=userName;
}

protected String getUserName() {
return userName;
}

protected void setMessage(String message) {
this.message=message;
}

protected String getMessage() {
return message;
}

public static void main(String args[]) {

netSend t=new netSend();
t.setUserName(args[0]);
t.setMessage(args[1]);
t.run();

}
}