One of the ways companies protect critical account information is by remembering the devices you use to log in as “trusted devices” or “authorized devices.” Those logins will usually have been protected by two-factor authentication or another mechanism that guarantees the device is being used by you, its owner. Subsequent logins from those devices may be more convenient for you due to requiring only a username and password, and trusted devices may automatically receive two-factor authentication codes. That’s how Apple ensures you are who you say you are when you log in to your Apple ID on a previously unseen device.
Although trusted devices can help increase your security, they can also reduce it. If an attacker were to gain access to one of your trusted devices, they would have a better chance of breaking into your accounts or masquerading as you when setting up new accounts. As a result, it’s important to audit your trusted devices occasionally and make sure you still control all of them. The first time you do this, you may be shocked to see that a Mac you last used years ago could still be receiving Apple ID verification codes. Removing unused trusted devices from an account makes it more secure with no downside.