One-Time Passwords have been introduced as a means of further securing your Square Enix account.

Digital drawing of a protective lock under the text 'Strengthen your account security with the One-Time Password system'
What is One-Time password?
Digital drawing of the Security Token and a smartphone using the Software Token A "One-Time Password" is a six-digit number shown on a screen using either a key-ring like the Square Enix Security Token or a smartphone app, such as the Square Enix Software Token.

What is a Security Token?
A security token is a device for displaying One-Time Passwords that will dramatically improve account security. Pressing the button will display a One-Time Password on the device's LCD screen which will provide you the required one-time password needed to access your account. Square Enix Security Tokens may be purchased from the Square Enix Store for $14.99.

Digital drawing of the front and back views of the Security Token, along with a table of its dimensions

What is a Software Token?
Digital drawing of 3 smartphones using the Software Token The Software Token is a smartphone app designed to display One-Time Passwords. After registering for the service, a One-Time Password will be shown on screen every time the app is launched. Using this app will dramatically improve account security. The app itself is free to use.
The app can only be used by customers with Square Enix accounts who have purchased either FINAL FANTASY XI or FINAL FANTASY XIV and registered the accompanying registration codes.

What is a Software Authenticator?
Software authenticators (Google Authenticator, Microsoft Authenticator, etc.) are free apps developed for smartphones (iPhone or Android) for the purpose of displaying one-time passwords.