FourEyes allows network administrators to enforce a four-eyes policy on Windows NT, 2000 and XP by requiring two users to authenticate during a local logon. A user can only use the computer if another user (the observer) also enters their username and password (or other authentication information). FourEyes does not include an authentication subsystem. It uses the existing software and hardware for authentication. This may include passwords, smart cards, tokens, biometrics or any other authentication technology.