When iOS or Mac connects to wifi, it hits a similar URL to Apple to check if the device is stuck behind a captive wifi network. If the check failed, it attempts to throw up the networks login page.
But Apple's check server went down, and therefore peoples iPod touches, Macs and iPads got stuck in a nasty cycle of trying to throw up a non-existant login page.
Actually it wasn't that the server was down, it was that it was misconfigured and returned unexpected 404 responses which made it look like a captive portal.
When iOS or Mac connects to wifi, it hits a similar URL to Apple to check if the device is stuck behind a captive wifi network. If the check failed, it attempts to throw up the networks login page.
But Apple's check server went down, and therefore peoples iPod touches, Macs and iPads got stuck in a nasty cycle of trying to throw up a non-existant login page.