security filter

In communications security, the hardware, firmware, or software used to prevent access to specified data by unauthorized persons or systems, such as by preventing transmission, preventing forwarding messages over unprotected lines or circuits, or requiring special codes for access to read-only files. [From Weik ’89] 2. [An] Information-system (IS) -trusted subsystem that enforces security policy on the data that passes through it. [INFOSEC-99]