Determine Whether a URL Is Valid

public static bool checkUrl(string url) 
{
  bool rt = false;
  if (url.StartsWith("www."))
  {
   url = "http://" + url;
  }
  HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(url); 
  HttpStatusCode code = new HttpStatusCode(); 
  HttpWebResponse myResponse = null; 
  try
  { 
   myResponse = (HttpWebResponse)myRequest.GetResponse();
   code = myResponse.StatusCode;
   rt = true;
  }
  catch(WebException err)
  {
   rt = false;
  } 
  return rt;
}