The D-Link DIR-615 has no logout option, and if you go to the admin URL's
(e.g. at any time after logging in, it lets you in
again without a password. This survives router reboots and even clearing
browser cache and cookies.

This is because the DIR-615 caches valid logins by MAC address -- i.e. if it's
seen a valid login from aa:bb:cc:dd:ee:ff, it lets that computer have unrestricted
access to the admin pages for a while (even if it changes IP addresses).