Well it turns out that the DSL-2680 does NOT have a hidden SSID hard wired into it.
I registered my unit with D-Link (I was already registered):
http://www.dlink.eu/support/ssplogin.html
This portal is heavy on Java and Firefox 24.0 doesn't like it. Instead use IE10 to see all the menus some of which disappear under FF.
I raised a case referring to what had been said here. The first response by them was to introduce me to inSSIDer v3 via a link. As soon as the instrumentation was launched I could see that the mysterious 'hidden' SSID did in fact come from a Sagecom WAP with a very weak 90dBm signal.
So I again hid my SSID and this is where things got interesting. InSSIDer displays at first a channel without an SSID. After hiding the SSID two channels appeared: one with my own SSID and a hidden channel.
I had no problems connecting the TV although I had to do it manually entering the SSID, password and encryption (AES). The only device that could not be connected was my Kindle touch mono e-reader. It wouldn't let me enter an SSID. In other words it didn't know about hidden SSID.
I wouldn't say I live a sheltered life but when it comes to microwave router smog, I do. InSSIDer revealed that mine was the only Wifi point in my neighbourhood with two more very weak points coming and going. Fortunately, the stronger unhidden SKY SSID was being picked up by the TV otherwise I would not have seen anything.
Out of interest today I took my laptop with me whilst my wife drove to my daughter who lives only a mile away. As soon as I left my vicinity the screen filled up with loads of wireless points' dozens of them. I was amazed at the number that were unsecured most of them BT but they could have been hot spots.
Had I lived just a bit nearer to this wifi smog I would have immediately twigged what was going on? But on my journey through this smog I never saw a single hidden channel wifi point – so much for strong security.
Just a note of caution on Win8 and inSSIDer, Win8 at first displays 'hidden network', you connect to it but the words 'hidden network' remain making you think that the router is sending out more than one channel. It isn't!
Whilst Windows has logged you onto a previously hidden channel it doesn't have the sense to realise that hidden network has the same MAC address as the one you previously connected to.
The danger is you might again try to connect using the same SSID – it will fail. The same applies to inSSIDer. It sees the hidden channel and the one you connected to but you can see that the MAC addresses are the same. Makes sense from an instrumentation point of view.
You will have fun playing around with hidden SSID, I know I did. Could not have sorted this without inSSIDer:
http://www.metageek.net/products/inssider/
Try it its free.