Proprietary software is software controlled by a vendor, where source code and internal design details are usually kept private. Users may run the product, but they generally cannot inspect, modify, or redistribute the code without permission. In cyber security, this matters because trust depends on the vendor’s engineering, patching, and disclosure practices rather than on public code review.
Attackers often do not need source code to abuse proprietary software; they look for weak update mechanisms, misconfigurations, exposed management interfaces, or flaws in bundled components. Defenders reduce risk by verifying signed updates, limiting privileges, isolating critical systems, and tracking vendor advisories and patches. Proprietary software can be secure, but only when it is governed well and defended like any other high-value attack surface.