//sub-method of urlTesterThread
        private void VerifyURLs()
        {
            for (int i = 0; i < active_urls.Length; i++)
            {
                if (urlTesterThread_shouldStop)
                {
                    break;
                }

                active_requests[i] = UrlTester.TestUrl_Async(active_urls[i], i, this);
            }
        }
        private bool CanConnectToInternet()
        {
            string            message = "No Internet connection found, the program is not able to verify the URLs.";
            string            caption = "No Internet connection found!";
            MessageBoxButtons buttons = MessageBoxButtons.RetryCancel;

            while (!UrlTester.CheckForInternetConnection())
            {
                DialogResult result = MessageBox.Show(message, caption, buttons);
                if (result == DialogResult.Cancel)
                {
                    return(false);
                }
            }
            return(true);
        }