Top arms groups are on high alert to counter cyber spies from stealing their own secrets at a major arms bazaar outside Paris, even as they market new ways to clients on how to repel hackers in the digital battle space. France is hosting the world’s largest arms fair for land forces near Paris airport Charles de Gaulle, attended by up to 50,000 people who make, buy and use advanced weapons. Its final day is today, June 18. The crowded arms bazaar is a snooper’s paradise and another proving ground for the cyber war which is already testing the resources of major-league defense companies. “It is very easy to go crawling over everybody’s systems here. Some people come and their approach is to grab everything they can,” said a senior Western defense company official. “There are two approaches — they either try to take the whole haystack and look for a needle, or there are those who know exactly what needle they are looking for.” Scouting out the competition is as old as trade fairs themselves, but the biennial Eurosatory arms gala brings together sensitive targets from the United States, Europe, Russia and — for the first time this year — China. Risks at the Eurosatory arms show range from petty theft to covert photography and electronic eavesdropping. Behind the suits and dark glasses there is an atmosphere of mutual distrust. Exhibitors are careful not to bring classified material into a show. But portable computer networks contain commercially sensitive information and may betray a useful signature that could later provide a side door into more sensitive systems.