In this case, nothing. The "attack" was a standard credential stuffing attack (https://en.wikipedia.org/wiki/Credential_stuffing https://en.wikipedia.org/wiki/

In this case, nothing. The "attack" was a standard credential stuffing attack (https://en.wikipedia.org/wiki/Credential_stuffing https://en.wikipedia.org/wiki/Credential_stuffing). Attackers were just using credentials that were leaked in other data breaches to access Nintendo Accounts (Switch and mobile apps), by logging in via a linked Nintendo Network ID (3DS and Wii U). If the password for your NNID had not been breached in the past (and then reused for the NNID), you wouldn't have been vulnerable. Enabling 2FA would also have protected you against this attack. Nintendo has solved this by: a) Resetting NNID passwords when they think someone has been affected b) Disabling the option to log in to Nintendo Accounts using the NNID username/password.