The revelation that a computer worm disabled a safety system in a US nuclear power station in January has led to fresh calls for security on electricity grids to be overhauled, according to New Scientist.

Experts say much of the grid’s critical infrastructure is too accessible to the virus-ridden public Internet.

When the Davis-Besse nuclear power plant in Ohio was hit by the Slammer worm this year, the reactor happened to be offline. But the worm disabled a safety monitoring system for nearly five hours. “We are still working through the information to find out what happened,” says a spokesman for Akron-based FirstEnergy, which owns the plant.

Some sources suggest the worm may have entered the plant’s network via a connection to an insecure network. But critical systems like power stations should be cut off from the outside world and the Internet, says Joel Gordes, a grid expert at Environmental Energy Solutions in Riverton, Connecticut. But this is not seen as a practical option in today’s cost-conscious and highly competitive energy market.

New Scientist press release