There is Currently No Evidence that Nintendo Database has been Breached
Earlier, Nintendo sent out a Japanese confirmation that about 160,00 Nintendo IDs have been compromised. They suspect that the intruder has access to both the login account and the passwords to access these IDs, and will be forcing the users of these accounts to change their passwords.
In an update, they mention that there is currently no evidence that their database has been breached. The official statement says that the Nintendo IDs were obtained through sources outside of their service. Which outside sources, they have yet to confirm.
Even if you were notified that your account was compromised, it is never a bad idea to reset your passwords after a security breach. We would recommend for all those with Nintendo IDs to switch their accounts as soon as possible.
Below is the official English statement provided by Nintendo:
We would like to provide an update on the recent incidents of unauthorised access to some Nintendo Accounts.
While we continue to investigate, we would like to reassure users that there is currently no evidence pointing towards a breach of Nintendo’s databases, servers or services. As one action in our ongoing investigation, we are discontinuing the ability to use a Nintendo Network ID to sign in to a Nintendo Account. All other options to sign-in to a Nintendo Account remain available.
As a further precaution, we will soon contact users about resetting passwords for Nintendo Network IDs and Nintendo Accounts that we have reason to believe were accessed without authorisation.
In addition, we also continue to strongly encourage users to enable two-step verification for their Nintendo Account as instructed here: How to set-up two-step verification for a Nintendo Account.
If any users become aware of unauthorised activity, we encourage them to take the steps outlined in the article about the Nintendo Account recovery process.
During the investigation, in order to deter further attempts of unauthorised sign-ins, we will not reveal more information about the methods employed to gain unauthorised access.
We apologise for the inconvenience and concerns caused to our customers, and we will continue working hard to safeguard the security of our users’ data.
Source: NintendoEverything