This is a "warning" news. It is in fact a few hours ago the news that ALMENO 450 account of the Nintendo Network used to access the online services of Wii U and 3DS (and to shop on the Nintendo eShop pages) have been violated by a handful of hackers.
First, check that you are not on the list of hacked accounts that you can find HERE.
Secondly, under the circumstances, it is highly recommended to change your passwords for Nintendo Network accounts, also because it is not absolutely certain that the violated accounts are only those made known.
Nintendo has not yet commented on the matter, we are therefore awaiting official statements even if, rightly, can not do anything but forward the usual phrases of circumstance containing excuses, etc. ... We take this opportunity, once again, to express dissent to acts of Gender: we respect and promote information technology with counter-attacks, even the so-called hackers at V for Vendetta or Anonymous. An account, however, is to show your skills (aka wanting to make the sboroni) "fighting" the system, an account making i THIEVES. That perdition collapses.
We hope to have been useful, let us know your problems!