A CYBER attack on the offshore industry could cost oil and gas firms billions of pounds in lost revenue, an expert warned yesterday.

And security experts say a computer-based attack by hackers, activists or even hostile nations on North Sea oil and gas production is now just a matter of time.

Cheryl Martin, director for UK cyber security at consultants CGI Group, said firms must be ready to defend themselves - or face the potentially crippling consequences. She said oil and gas platforms had already been targeted but so far no-one had breached tightened security measures. "These 'hack-tivists' and activists would be delighted to take over the production on an oil rig," she said. "Every industry has failed to catch up with this threat and hackers and activists are ever-developing.

"They are always one or two steps ahead. That's why it's not a question of if you are going to get attacked - it's a question of when.

"It's then, 'how do you stop that attack or mitigate it?' These attacks could cost in the billions of pounds."

The warning comes after a global survey of oil and gas firms by PwC found that information security budgets averaged five million pounds in 2013.

Disgruntled former employees were also identified as possible threats to security during a summit in Aberdeen where Ms Martin was a key speaker. Cyber attacks on oil and gas firms rose above 6,500 cases last year, she added.