Prof David Stupples, who advises the government, told the BBC that plans to replace ageing signal lights with new computers could leave all of Britain's trains exposed to cyber-attacks.

Network Rail, which is in charge of the upgrade, acknowledges the threat.

"We know that the risk [of a cyber-attack] will increase as we continue to roll out digital technology across the network," a spokesman told the BBC.

"We work closely with government, the security services, our partners and suppliers in the rail industry and external cybersecurity specialists to understand the threat to our systems and make sure we have the right controls in place."

Critical systems that control the speed and stopping of trains could be compromised. The system is already in use in other parts of the world, making driver mistakes a thing of the past.

But, says Prof Stupples - an expert in networked electronic and radio systems at City University in London - "Certain ministers know this is absolutely possible (to hack the system) and they are worried about it. Safeguards are going in, in secret, but it's always possible to get around them."

The system is pretty well guarded against outside attacks, but insider attacks could still be possible.

"The risk is that staff will either be deliberately and clandestinely assisting attackers or - most likely - make poor decisions, such as plugging in a device that is malware-infected that could expose the system's security."

Source: BBC.com