There have been around 160,000 accounts that have been hacked.
Nintendo says they have reset all the passwords for accounts that have been viewed by a third-party. But as always, everyone should change their passwords and as a 2nd security measurement, please use two-step verification to secure your account.
The information that could have been stolen is the nickname, date of birth, country, and email address. Most likely the credit card details are still secure, but it does not harm to check the credit card bill.
As a Security recommendation from Onono, always use two-step verification where it is possible.
Info reported by Nintendo