Linked devices are companion sessions that connect a messaging account to additional phones, tablets, or desktops while sharing the same account context. They are meant to make multi-device use easier, but they also widen the attack surface because a single account can have several active endpoints at once.
In cyber security, linked devices matter because compromise is not always limited to the main phone. If an attacker gains access to one session, they may be able to read synchronized messages, send messages as the victim, or keep access even after the primary device is cleaned. For incident response, investigators should check every paired device, review session history, and revoke unknown links. Defenders should also alert on new pairings, require re-authentication for sensitive actions, and remind users to remove old or unused companion devices.