The rattling of cyber swords could be heard today as the Pentagon confirmed computer hackers had gained access to an unclassified e-mail system in the office of Defense Secretary Robert Gates, but then declined to say the Chinese army was responsible for it. The Financial Times this week quoted current and former U.S. officials as saying that Chinese People’s Liberation Army hackers broke into a Defense Department network in June and removed data. Pentagon spokesman Bryan Whitman said that an attack did occur in June but declined to identify the origin of the threat. It is often difficult to pinpoint the true origin of an intrusion into computer systems and even more difficult to tie the intrusion to a specific nation or government, he said. The system impacted was taken down for over a week, reports said.There are hundreds of attempted intrusions into the Defense Department computer network each day, the majority of which are detected and stopped, Whitman said. The nature of the threat is large and diverse and includes recreational hackers, self-styled cyber vigilantes, various groups with nationalistic or ideological agendas, transnational actors, and nation states. When appropriate, the department turns cases over to law enforcement officials for investigation, he said. "We continue to aggressively monitor our networks for intrusions," Whitman said. "We have appropriate procedures to address events of this nature." "Cyber or non-kinetic type threats to military computer networks are viewed as just as real and just as significant as physical or kinetic threats," Whitman said. "The department aggressively responds to deter all intrusions to defend what is known as the GIG, the global information grid." China rejected story completely. Security watchers are on edge about this matter in the wake of the recent denial-of-service (DOS) attacks against Web sites in Estonia which started around April 27, and have crippled Web sites for Estonia's prime minister, banks, and less-trafficked sites run by small schools, said Hillar Aarelaid, CSO for Estonia's Computer Emergency Response Team. Most of the affected Web sites have been able to restore service. A homeland security official told Network World recently national cyber attacks might rise but said such happening are few and far between.