Security researchers who took control of two popular vehicles by connecting a laptop to their internal computers moved a step closer to one day being able to secretly commandeer a car from the driver, experts say.

By connecting cables to the cars' electronic control units, the researchers were able to use the software they developed to steer left and right, apply the brakes and move the fuel gauge to zero, the BBC reported. The test was performed on a 2010 Ford Escape and a Toyota Prius.

The vehicles' manufacturers did not consider the work a hack. That's because the proof of concept, by Charlie Miller, a security engineer at Twitter, and Chris Valasek, director of security intelligence at IOActive, required a wired connection with the intruder in the vehicle.

However, that logic misses the point, security experts said Monday. Just because no one has been able to commandeer a vehicle by wirelessly hacking into its internal computers does not mean it won't happen eventually. Miller's and Valasek's experiment shows that experts are getting closer.

"What they're showing is every time they take a step, they're taking a new step forward," said Glenn Chisholm, vice president of product management and chief security officer of Cylance.

In 2010, researchers from Rutgers University were able to wirelessly hack a car's tire-pressure monitoring systems and send a false low-pressure warning. The bogus signal was sent from a car traveling behind the target vehicle.

Of course, breaking into such a system is not nearly as complex as wirelessly hacking an ECU, which are embedded systems that control steering, acceleration, braking and other critical functions.

Nevertheless, the 2010 experiment showed a wireless hack is possible, and the latest research demonstrates would could be done if an ECU is breached.

[Also see: Computerized conveniences make cars the next target for hackers]

The fact that the Defense Department's research facility DARPA funded the latest work shows that the government believes that the growing number of computer systems going into vehicles could present a safety threat.

"I believe that the digital attack surface for vehicles will undoubtedly increase in the coming years, and the fact that DARPA chose to sponsor Valasek's and Miller's work is a good indication that they see this field growing in importance," Aaron Portnoy, vice president of research for Exodus Intelligence, said.

Car manufacturers insist they are paying close attention to security. Toyota told the BBC it has developed "very strict and effective firewall technology" against wireless attacks. Ford says "safety, privacy and security of our customers is and always will be paramount."

Andrew Ginter, vice president of industrial security at Waterfall Security, said carmakers could learn from the practices of the nuclear power industry.

Monitoring systems are on one network while systems that control reactor operations is on a separate network that's closed to the outside. Ginter suggested the same architecture for vehicles where separate computers are used for monitoring and for critical functions, such as brakes, acceleration or steering.

"If they're not connected, then the only thing you can hack over the network is the monitoring functions," Ginter said. "The safety critical functions continue to work."

Miller and Valasek are scheduled to present details of their work this week at the Defcon security conference in Las Vegas.

Read more about application security in CSOonline's Application Security section.