how to check the url(url fake or not) in a windows web browser?

if (url != "")
{
UriBuilder uriBuilder = new UriBuilder(url);
HttpWebRequest request = HttpWebRequest.Create(uriBuilder.Uri);
HttpWebResponse response = request.GetResponse();
if (response.StatusCode == StatusCode.NotFound)
{
// URL Not Found
}
if (response.StatusCode == StatusCode.OK)
{
// Valid URL
}
}
code error in windows form application