An improved computer network security system and a personal identifier device used for controlling network with real time authentication of both a person's identity and presence at a computer workstation is provided. A new user is registered to a portable personal digital identifier device and, within the portable personal digital identifier device, an input biometric of the user is received and a master template is derived therefrom and securely maintained in storage. A private key and public key encryption system is utilized to authenticate a user registered to the portable personal digital identifier device. The personal digital identifier device verifies the origin of a digitally signed challenge message from the network security manager component. A digitally and biometrically signed challenge response message is produced and transmitted by the personal digital identifier device in response to the verified challenge message.