Linked device
In a messaging service, a linked device is an additional endpoint associated with an account so it can participate in that account's messaging, subject to the service's capabilities and settings.
Linking a desktop messaging app lets someone use their account from another device. It is an account-access decision. It is not the same as joining a group, adding a contact, or enrolling a computer in an employer’s device-management system.
Encryption still needs the right endpoints
Signal devices share account identity keys, but each linked device has independent keys for message encryption. A newly linked device can receive messages, and the linking process can optionally transfer existing message history. The precise behavior belongs to Signal; other messengers have their own rules.
End-to-end encryption protects communication between participating endpoints. It does not establish that the account owner intended to add a particular endpoint. A deceptive invitation can therefore abuse a legitimate linking feature without breaking the encryption.
Before linking, establish which device is being added and who controls it. A QR code presented as a group invitation should not require an account-level device-linking action. Our messenger article explains that mismatch and the reported campaigns that used it.
If an unfamiliar device appears in the account’s linked-device list, use the service’s removal process and report the event. Removing its future access does not establish what it already received or copied. The QR reporting article explains how to preserve the original invitation and the phone-side action without sharing sensitive account material.