People should plan for potential cyber-attacks by going back to pen and paper, according to the latest advice.
The government has written to chief executives across the country strongly recommending that they should have physical copies of their plans at the ready as a precaution.
A recent spate of hacks has highlighted the chaos that can ensue when hackers take computer systems down.
The warning comes as the National Cyber-Security Centre (NCSC) reported an increase in more serious cyber attacks this year.
Criminal hacks on Marks and Spencer, The Co-op and Jaguar Land Rover have led to empty shelves and production lines being halted this year as the companies struggled without their computer systems.
