Not even Nintendo is safe from server attacks, but nothing was lost.
As you may or may not know, Nintendo’s online services require you to enter your credit card (or other) information anew every time you want to purchase something from there. While a lot of people have complained about this rather inconvenient way of dealing with it, it has basically just saved Nintendo’s ass. Because of how they handle things at the moment, there was no personal data on anybody to be found on Nintendo’s servers. The hacker group calling themselves LulzSec, who have been attacking lots of Sony servers as of late have admitted to being the culprits this time as well and confirmed that they got nothing. Just a short while later Nintendo closed the hole that let them be hacked in the first place, which was also confirmed by the hackers responsible.
Say what you will, but Nintendo does a good job of keeping things safe.