If you were affected, illegal purchases will be immediately cancelled. (UPDATING)
Nintendo has confirmed the number of accounts affected by a recent breach and has begun mitigation steps.
According to Nintendo, more than 160,000 accounts were affected by the breach of the Nintendo Network ID service. Nintendo Network ID login has been disabled, and affected users will have forced password resets for both their NNIDs and Nintendo Accounts. Users are encouraged to use new passwords and enable the 2-factor authentication on their Nintendo accounts.
The company has encouraged any users who had "illegal"/unauthorized purchases made on their accounts to contact them for cancellation. Currently, the breach is being quoted as beginning earlier this month.
Although the breach did not expose credit card information directly, user dates of birth and emails were accessible and full names were potentially accessible if one was applied.
Nintendo of Europe has posted a similar statement on their support pages. Notably, the statement denies that Nintendo's systems were breached.