The first-ever, cross-European simulation of an all-out cyberattack, conducted last week, was intended to help expose flaws in existing plans to combat such attacks, the BBC reported.
The test was an "important first step towards working together to combat potential online threats to essential infrastructure," Neelie Kroes, the European commissioner for the digital agenda, said.
As the simulated attacks escalated, cybersecurity centers had to find ever more ways to keep Internet traffic flowing to key services and sites.
The simulated exercise was overseen by the European Network Security Agency, recently given new powers to help member states handle cybersecurity incidents.
Twenty-two EU member states along with Iceland, Norway and Switzerland took part in the simulation, the BBC said.