Nintendo recently announced that the Nintendo Network will be undergoing "emergency maintenance" beginning today at 3:00 PM Eastern (11:00 PM Pacific). The behind-the-scenes work will apparently result in intermittent interruptions to a variety of games and online services.
Here's the full emergency maintenance breakdown straight from Nintendo:
From Monday, January 28, 2013 11:00 PM - Tuesday, January 29, 2013 5:00 PM Pacific Time
Pokémon Black Version
Pokémon White Version
Pokémon Black Version 2
Pokémon White Version 2
From Monday, January 28, 2013 5:00 PM - Monday, January 28, 2013 6:00 PM Pacific Time
Match Making, Ranking, etc.
Warriors Orochi 3 Hyper
From Monday, January 28, 2013 12:00 PM - Monday, January 28, 2013 5:00 PM Pacific Time
Wii Shopping Channel
Nintendo DSi Shop