I have a Samsung Smart TV, which has worked well for 18 months. Today I used itv Player and All4 without a problem, then later in the day tried to access BBC iplayer, and itv Player, YouTube, All4, netflix, etc. Not one app will open, except for Demand 5. The settings tell me that the Internet is not connected, but Demand 5 is still loading and playing! I have tried resetting the Internet and the TV several times to no avail. Has anyone else had this issue?

Yes, it seems the smart hub servers were down across a number of countries last night

Thanks! Where did you find out this information from? It all still seems to be not working this morning.

Was on twitter last night, problems across UK and USA, and problems reported in other countries too.

Some people had luck changing their DNS servers,

http://www.product-reviews.net/2015/...-for-problems/

Just seen your post
I had this problem last night .Did everything you did. Today it is working O.K. I did ring Samsung earlier, before realising it had affected so many people.. I should have asked them if anyone else experienced the same problem? They just said did I update my TV? I said no, I did not realise. So I updated it anyway.
I have had this happen a few times before, but normally I just did retry, and it would go back to normal. I think a few weeks ago one Sunday evening it was like that for a while then back to normal.