The simulation steadily reduced access to critical services to gauge how nations react. The exercise also tested how nations work together to avoid a complete shut-down of international links.
Neelie Kroes, European commissioner for the digital agenda, said the exercise was designed to test preparedness and was an "important first step towards working together to combat potential online threats to essential infrastructure".
The exercise is intended to help expose short-comings in existing procedures for combating attacks. As the attacks escalated, cyber security centres had to find ever more ways to route traffic through to key services and sites.
