In response to recent incidents related to some Nintendo Accounts, Nintendo has officially discontinued Nintendo Account sign-ins using a Nintendo Network ID. Read on below to learn more:
Nintendo Network ID Sign-In Discontinuation to Nintendo Account
Applies to: Nintendo Account
We would like to provide an update on the recent incidents of unauthorized access to some Nintendo Accounts.
While we continue to investigate, we would like to reassure users that there is currently no evidence pointing toward 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 authorization.
In addition, we continue to strongly encourage users to enable 2-Step Verification for their Nintendo Account.
If any users become aware of unauthorized activity, we encourage them to follow the steps in the Nintendo Account recovery process.
During the investigation, in order to deter further attempts of unauthorized sign-ins, we will not reveal more information about the methods employed to gain unauthorized access.
We apologize for the inconvenience and concerns caused to our customers, and we will continue working hard to safeguard the security of our users’ data.
Source: Nintendo Support
Pokémon Blog 
One thought on “Nintendo Account sign-ins using Nintendo Network ID discontinued following incidents of unauthorized access”