This is the url all iOS devices request as soon as they are connected to wifi. And It is currently down.

Edit: It is back now. And this is the response:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
    <HTML>
    <HEAD>
	    <TITLE>Success</TITLE>
    </HEAD>
    <BODY>
    Success
    </BODY>
    </HTML>