, a Japanese defence contractor, has been hit by over 50 separate computer viruses, causing concern that vital security information may have been compromised.
One computer was infected by 28 separate types of virus, including ones that could have been prevented with existing anti-virus software, Japanese newspaper the Yomiuri Shimbun said, amid concerns over the security of defence information.
In the wake of the information coming to light, the Japanese defence ministry plans to tell Mitsubishi Heavy to file detailed reports on its cyber security measures, the newspaper says.
Mitsubishi Heavy is analysing 83 computers hit by the attacks and has found more than 50 kinds of viruses, significantly more than the eight strains that the company had previously reported.
The company reportedly declined to comment on the story while officials could not be reached for immediate comment.
Japan’s defence minister said in September there was no indication that sensitive information had been stolen as a result of the attacks on the firm’s computers, which came to light in August.
The Yomiuri earlier reported that the attackers may have used Chinese-language script in creating the viruses.
China has frequently been accused of spearheading online attacks against companies and government agencies, although Beijing has always denied these allegations.
Earlier this year, internet giant Google said a cyber-spying campaign originating in China had targeted the Gmail accounts of senior US officials, military personnel, journalists and Chinese political activists.
US Deputy Defence Secretary William Lynn claimed that a foreign intelligence agency was behind an attack that stole classified information on a top secret weapons system. The incident was one in a series of attacks against American defence contractors.
These kinds of cyber-attacks recently saw the chairman of the US House Intelligence Committee, accuse China of stealing some of America’s most important industrial secrets.
In hearings conducted by the committee Congressman Mike Rogers said Chinese cyber-spying had reached an “intolerable level”.
“I don’t believe that there is a precedent in history for such a massive and sustained intelligence effort by a government to blatantly steal commercial data and intellectual property,” he said at the hearing, adding later, “I feel very comfortable saying that Chinese nation-state activities have led to the exfiltration of intellectual property at a staggering rate.”
His sentiments were backed up by former CIA and NSA director Michael Hayden, who claimed he was “in awe at the breadth, depth, sophistication and persistence of the Chinese espionage effort against the United States of America”.
The relationship between Japan and China has often been fractured, with a dispute over islands claimed by both nations threatening to escalate into full-blown conflict in late 2010.