Soon, Ragnar Rattas and his team of Estonian computer security experts were battling the heaviest and most sophisticated cyber attacks they had ever encountered. As the situation worsened, they abandoned some networks – including a major public facing website – to protect the networks that kept vital data and industrial systems running in the research center they were defending. Meanwhile, they faced a growing media storm as they raced to discover where the assault had come from. It was, fortunately for them, just an exercise – a major game dubbed Locked Shields run on March 21-22 by the NATO Cooperative Cyber Defence Centre of Excellence in Tallinn, Estonia. With more than 300 participants and teams from 17 nations, organizers said it was the largest international cyber maneuver yet mounted, simulating an attack on a fictional nation called Berylia by a 50-strong team of computer experts. Companies and nations are pouring ever greater resources into cyber security, including sophisticated simulations, as they worry over data and intellectual property theft as well as attacks causing physical damage. In 2012, the worlds largest oil producer Saudi Aramco suffered a cyber attack that damaged some 30,000 computers while experts believe the United States – and perhaps Israel – used the Stuxnet worm to make some of Irans nuclear centrifuges tear themselves apart. Despite rising tensions since Russias annexation of Ukraines Crimea region, organizers said Locked Shields was not directly aimed at simulating any action by Russia. The increasing sophistication of recent exercises, experts say – and the murky overlapping mix of criminal, state and other forces – point to the ever-growing complexity of confrontation. It was very challenging, team leader Rattas, who runs the critical infrastructure protection team at the Estonian Information System Authority, told Reuters. They were very sophisticated attacks.