Old revisions Add to book Export to PDF Fold/unfold all Book Creator Add this page to your book Book Creator Remove this page from your book Manage book (0 page(s)) Help Firewall A security system used to prevent information leakage and system damage caused by unauthorized, external access to a network used by PCs belonging to individuals or an organization. A firewall is located at the boundary between the external Internet and the internal private network, and permits or blocks external access attempts according to a preset access control list.