A linked device is a secondary phone, tablet, computer, or session that has been paired with a primary account, such as a messaging app, email account, or cloud service. Once linked, it can receive messages, sync data, or access account functions without requiring the main device every time. That convenience also creates risk: if an attacker adds an unauthorized linked device, they may quietly read communications, intercept verification codes, or maintain access even after the original device is protected.
In cyber security, linked devices matter because they expand the attack surface beyond the handset itself. Attackers may abuse stolen credentials, phishing, or account recovery weaknesses to bind a new session, then hide inside normal account activity. Defenders should regularly review active sessions, remove unknown devices, require strong authentication, and monitor for unexpected pairing prompts or account-change alerts. In mobile espionage, checking linked devices is often as important as scanning the phone for malware.