Europe needs to do more to prepare itself for cyber attacks, an EU report has concluded.
The judgement follows a simulation of how member states would deal with a sustained attack on their networks.
The simulation tested how countries would cope if international net connections failed to work, leaving citizens, businesses and public bodies unable to access online services.
Future tests must involve the private sector, the report said.
Cyber Europe 2010, a so-called "cyber stress test", aimed to give member states better understanding of how to handle such cyber incidents and create best practices for the future.
Organisers said that while the exercise met its stated aims, it revealed that more still needs to be done.
"Member states need to do more with their national security exercises," said Ulf Bergstrom, a spokesman for the organisers, the European Network Security Agency (Enisa).
"Not enough member states are doing such exercises and they must increase their efforts."
"Countries need proper policies about what to do if channels break down, how communications will function and what the roles and responsibilities are," he added.
The report also concluded that future simulations should include the private sector.
"The networks are largely owned by the private sector and they should be involved," said Mr Bergstrom.
A pan-European cyber attack is a real possibility, Mr Bergstrom suggested.
"All systems are interconnected and cross national boundaries. These networks are crucial for the European economy and that is why are are co-operating at a European level," he said.
There were 30 European countries involved in the European simulation.
A full report into the exercise will be published at the beginning of next year.
UK Defence minister Nick Harvey said this week that it was just "a matter of time" before terrorists used the internet to launch an attack.
The UK plans to spend £650m over the next four years on a National Cyber Security Programme, aimed at protecting individuals and the national infrastructure from hostile computer attacks.