Second-hand software is previously licensed software that is resold or transferred from one owner to another. In legitimate markets, the buyer is not getting a new copy from the vendor; they are acquiring existing usage rights, which may depend on whether the licence is perpetual, transferable, and allowed in the relevant jurisdiction.
This matters in cyber security because entitlement data is part of the trust boundary. Defenders need to know exactly who owns a licence, whether it was lawfully transferred, and whether activation media or keys are authentic. Attackers and fraudsters can exploit weak records by selling counterfeit licences, reusing stolen keys, or misrepresenting transfer rights. For organizations, careful asset inventory, contract review, and document retention help prevent compliance failures and reduce the risk of buying untrusted software.