Abstract: The invention relates to a device that is placed in a computer network for securing the communication flows passing through the device. The communication flows are secured using portable codes, known as portable agents, which can be downloaded from a remote terminal. The portable agents cannot be executed by the device until they have been compiled by a compiler which is present in the device, at which point they become executable agents. The compiler translates the portable agents, which are written in a language that is independent of the processor, into executable agents written in the language of the processor of the device, while placing controls on the functions performed by the agent. The executable agents are then executed in the device in accordance with the communication flows passing through it and a security policy, which can also be downloaded from a remote terminal.