I have been getting this a lot the past week and was wondering what it attributes too. I'll just be playing in my passworded game with my necro leveling my merc and all of a sudden this msg will come up.
There are essentially two cases for realm down that I've experienced, the most common being that you are logging in/creating games in quick succession.
I've also gotten realm down when a game crashed, followed by "lost connection to battlenet" and "realm down". This usually doesn't last long, though. It DOES NOT happen on all game crashes, just occasionally (and it's server-side crashes, not client-side crashes).
can't you also get realm downed if Blizzard suspects you are suing maphack or something? or is just a straight away ban? The main point is that maphack is bad.
i'm not trying to say you are using maphack or anything. just heard that somewhere.