I think this needs to be a POST request rather than a GET request with query params. GET seems a bit transparent for this sort of information. On agov.com.au I can see I've posted:

http://updates.agov.com.au/update_check?agov_register_agency=Chris%20Industries&agov_register_contact=Chris%20Skene&agov_register_email=chris%40previousnext.com.au&agov_register_notification=0&agov_register_id=43738a1e-435e-483f-8e04-1b6a613dd850

And Im concerned this leaves us open somewhat. Thoughts?

Obviously, we need to make sure this is SSL secured anyway.