check if a Yahoo! IM user is online

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO;

namespace YahooIM_User_Online_Check
{
    public static class YimIsOnline
    {
        /// <summary>
        /// Returns the state of a Yahoo IM user assuming user's are not using stealth settings.
        /// </summary>
        /// <param name="Username">Yahoo user name, should not include "@Yahoo.com"</param>
        /// <returns></returns>
        public static bool isOnline(string Username)
        {
            string isonval = PostData("http://mail.opi.yahoo.com/online?u=" + Username.Trim() + "&m=t&t=1");

            if (isonval == "00")
            {
                return false;
            }
            else if (isonval == "01")
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        private static string PostData(string url)
        {
            HttpWebRequest request = null;

                Uri uri = new Uri(url);
                request = (HttpWebRequest)WebRequest.Create(uri);
                request.Method = "POST";
                request.ContentType = "application/x-www-form-urlencoded";
   
            string result = "";

            using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
            {
                using (Stream responseStream = response.GetResponseStream())
                {
                    using (StreamReader readStream = new StreamReader(responseStream, Encoding.UTF8))
                    {
                        result = readStream.ReadToEnd();
                    }
                }
            }
            return result;
        }
    }
}