Blizzard made 2 announcements recently with the game breaking the all-time Day 1 sales record for a PC game at around 3.5 million copies and part of the reason for the servers being bombarded.
The other is the recent news of account hacking and Battle.net itself being attacked by saying the service itself hasn't been attacked nor has anyone's account been hacked in any new ways. They did say so far it seems to be mainly phishing attacks have been the cause for some accounts to become compromised.
http://www.giantbomb.com/news/blizza...promised/4170/
http://www.giantbomb.com/news/diablo...ay-alone/4169/