Zeeya Merali at Nature News writes: ''Quantum hackers have performed the first 'invisible' attack on two commercial quantum cryptographic systems. By using lasers on the systems — which use quantum states of light to encrypt information for transmission — they have fully cracked their encryption keys, yet left no trace of the hack.
<!--break-->Quantum cryptography is often touted as being perfectly secure. It is based on the principle that you cannot make measurements of a quantum system without disturbing it. So, in theory, it is impossible for an eavesdropper to intercept a quantum encryption key without disrupting it in a noticeable way, triggering alarm bells.
Vadim Makarov at the Norwegian University of Science and Technology in Trondheim and his colleagues have now cracked it. "Our hack gave 100% knowledge of the key, with zero disturbance to the system," he says.''

You can also find more information concerning the hack at the [http://www.iet.ntnu.no/groups/optics/qcr/hacking-commercial-quantum-cryp... Cracking commercial quantum cryptography: how we did it, in pictures] page.