Block any url address

private void button1_Click(object sender, EventArgs e)
        {
            String path = @"C:\Windows\System32\drivers\etc\hosts";
            StreamWriter sw = new StreamWriter(path, true);
            String sitetoblock = "\n 127.0.0.1 Your_url_for_blocking";
            sw.Write(sitetoblock);
            sw.Close();           
        }