I want to catch on the web page data in a row have a ImageButton, they are all in the UpdatePanel with ASP.NET AJAX submit, don't know how to crawl after click ImageButton content

PS: after clicking ImageButton, background processing will pop up after the completion of a web page, the web site will bring an encrypted after a string of a string, such as:
http://some_ip/some_page.aspx? Nid=MTYyMDUw
Because don't know how many MTYyMDUw is unable to grab the page data,