A legacy platform is older hardware or software that remains in active use after newer generations have arrived. In cyber security, these systems matter because they often run with limited patch support, outdated drivers, old authentication methods, or integration rules that were designed for a previous era. Even when a legacy platform still works, it may be harder to secure, monitor, and certify than current systems.
Legacy platforms appear in real environments whenever organizations delay upgrades, depend on specialized software, or keep backward compatibility for users. Attackers may target them because they can expose known vulnerabilities, weak configurations, or abandoned management paths. Defenders treat them as a risk-management problem: isolate them, restrict access, monitor them closely, and plan retirement or migration before support ends. In live services, dropping legacy hardware is often part of a controlled deprecation process, not a sudden failure.