Most of the time you can't, which is why so-called air-gapped computers are considered more secure than others.

More recently, evidence has shown that air-gapped systems can also be attacked through radio waves.

Because the computers are air-gapped from the internet, however, they cannot be reached directly by the remote attackers.

So the attackers had to devise ways to get the weapon onto those air-gapped machines.

So that's one machine is an air-gapped laptop.

The attack scenario they demonstrated is ideal for targeting air-gapped systems that can't be infected through network connections.

Crucial infrastructures use what's called an air-gapped strategy, where the control servers have no connection whatsoever to the public Internet.

Researchers in Israel showed how they could siphon data from an air-gapped machine using radio frequency signals and a nearby mobile phone.

Although these were air-gapped.

Oh, and the point was this was called AirHopper because this would be for air-gapped computers.

The spy agency has reportedly been using a more sophisticated version of this technique for years to siphon data from air-gapped machines in Iran and elsewhere.

Later in 2015, researchers introduced GSMem, a method for exfiltrating data from air-gapped computers over cellular frequencies.

The code was only supposed to work within Iran's Natanz refining facility, which was air-gapped from outside networks and thus difficult to penetrate.

This, and the use of attacks via USB flash drives, effectively mean that no air-gapped system is beyond the reach of attackers.

An air-gapped computer is one that is neither connected to the internet nor connected to other systems that are connected to the internet.

"We have some radios dedicated to the passenger cabin and some to the pilot, and these are air-gapped and don't cross over at all," he notes.

Bruce Schneier is even using it to store information on his personal air-gapped super-laptop, after he reviews leaked NSA documents.

But many companies insist that a network or system is sufficiently air-gapped even if it is only separated from other computers or networks by a software firewall.

Computer systems controlling the centrifuges were air-gapped, so the attackers designed Stuxnet to spread surreptitiously via USB flash drives.

In 1891 he developed various alternator apparatus that produced 15,000 cycles per second and developed his own very large air-gapped coil, known now as a Tesla coil.

One of the most famous cases involving the infection of an air-gapped system is Stuxnet, the virus/worm designed to sabotage centrifuges used at a uranium enrichment plant in Iran.

Researchers from Tel Aviv University and Technion have apparently found a way to gain access to private encryption keys from air-gapped computers while their equipment is in the other room.

It had characteristics of that; but all of it was about, we now know, arranging to get a specifically capable malware package installed on air-gapped machines that were controlling the refinement centrifuges in Iran.

If the concern is cyber vulnerability while the submarine is pierside in Faslane, we can only assume that the operating system also will be "air-gapped" and that malware cannot be imported into it via the net.

Outside contractors responsible for programming the systems in Iran were infected first and then became unwitting carriers for the malware when they brought their laptops into the plant and transferred data to the air-gapped systems with a flash drive.