(Reproduced from http://www.nature.com) Eavesdropping on the line Secure electronic communication is becoming increasingly important. In recent years, quantum cryptography has been investigated as a means of detecting eavesdroppers on private lines. When quantum mechanical processes are used to establish the 'key' used for encryption and decryption, any eavesdropping during transmission leads to an unavoidable and detectable disturbance in the received key information. This technique has been demonstrated to be effective on standard communication lines between two users, but Paul D. Townsend now introduces a practical scheme for a multi-user network. This work demonstrates the technical feasibility of quantum cryptography for practical applications. P D Townsend Quantum cryptography on multi-user optical fibre networks (Letter to Nature) Nature 385, 47-49 (1997)