..... a group from the Massachusetts Institute of Technology (MIT) in Cambridge was able to 'listen in' using a sort of quantum-mechanical wiretap. The trick allowed them to tease out about half of the data, in a way that couldn't be detected by those transmitting or receiving the message.
Still, all is not lost.
To grab the information en-route would require a 'quantum non-demolition box' - a theoretically possible but as-yet-unbuilt device that could measure the photon and pass it along. "What they have done is a simulation of an attack, not a real one," says Lo.
Shapiro and Wong agree. And they add that a quantum cryptographic network can be simply tweaked to beat their attack. By making the key out of a lot of photons instead of just a few, the sender and receiver could ensure that the eavesdropper never got enough of the key to use it. Still, they say, the work shows that secrets — even quantum ones — are never entirely safe.
 Kim T., et al. Phys. Rev. A, v.75 p.042327 (2007).