A network created by scientists in Austria is being claimed to be unbreakable.
The team in Vienna has managed to connect six locations across the city and the nearby town of St Poelten using 200km of standard commercial fibre optic cables.
But the network is claimed to be unassailable by outsiders as it is the first ever to use quantum encryption.
Here's the science bit - "Quantum cryptography is based on complex mathematical procedures which are extremely hard for outsiders to crack, but not impossible given sufficient computing resources or time. But quantum systems use the laws of quantum theory, which have been shown to be inherently unbreakable", (thank you Auntie).
This basically means that if someone tries to eavesdrop on a communications channel, the disturbance on the quantum information will show up.
The Vienna experiment sees photons fired a million times a second between six different "nodes", which are each housed in a different Siemens office.
In each of these locations, there is a small rack of electronics and a handful of sensitive light detectors.
Dr Hannes Huebel of Vienna University, which is operating one of the nodes, explained where the system may be used: "We are constantly in touch with insurance companies and banks, and they say it's nearly better that they lose 10 million euros than if the system is down for two hours, because that might be more damaging for the bank".
"So that's what we have to prove, that we have a reliable system that delivers quantum keys for several weeks without interruption, and then they might be more interested."