Abstract: A valve which prevents the filling of a fluid container through a port (6) by an unauthorized party, and, at the same time, allows the filling of the container through the same port (6) by an authorized party. The valve is operated by an actuator means (10) which controls the fluid flow through the valve. The valve combines two major features: (1) operation of the actuator means (10) is by an encoded device (32) whose code is known only to the authorized party; (2) the actuator mean is sealed within the valve housing or container so that physical access to the actuator means (10) is restricted. This combination of features makes the valve tamper-proof and actuatable by authorized parties only. Also disclosed is a valve system and a method for preventing unauthorized access to a fluid container.