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 Wii U and 3DS online services (and to make purchases on the Nintendo eShop pages) have been breached by a handful of hackers.

First, check that you are not on the list of hacked accounts that you can find HERE.
Secondly, given the circumstances, it is highly recommended to change your passwords for Nintendo Network accounts, also because it is absolutely not certain that the violated accounts are only those disclosed.

Nintendo Network

Nintendo has not yet commented on the matter, so we are waiting for official statements even if, rightly, it will not be able to do anything other than forward the usual circumstantial sentences containing excuses etc ... We take the opportunity, once again, to express dissent towards acts of the gender: we respect and promote computer scientists with counter balls, even self-styled hackers at the V for Vendetta or Anonymous. However, it is one thing to show your skills (aka wanting to make big shots) by "fighting" the system, another thing by doing the THIEVES. That perdition collapses.

We hope to have been useful, let us know your problems!