"US cyber security firm Mandiant's report is groundless both in facts and legal basis," Geng Yansheng, spokesman with the Chinese Ministry of Defence, told reporters at a media briefing.
China's armed forces had never backed any hacking activities, he said.
Mandiant released a report on Monday in which it alleged that a secret Chinese military unit in Shanghai was behind years of cyber attacks and has stolen data from 141 companies, 115 of which were in the US.
"Our research and observations indicate that the Communist Party of China (CPC) is tasking the Chinese People's Liberation Army (PLA) to commit systematic cyber espionage and data theft against organisations around the world," alleged the report called 'APT1: Exposing One of China's Cyber Espionage Units'.
Geng said Mandiant's report was groundless in fact because it came to the conclusion that the source of attack came from China simply because of the discovery that attacks were linked to IP addresses based in China.
As known to all, it is so common for hacking attacks on the Internet to take place by peculating IP addresses that "it happens almost everyday," state-run Xinhua news agency quoted Geng as saying.
There has been no clear and consistent definition of cyber attacks around the world. The report lacks legal basis to assert cyber espionage only by cataloguing some routine cyber activities, he said.
This is not the first time China has been accused of orchestrating the cyber attacks on other countries.
Beijing routinely denied such charges, saying that it too is a victim of cyber crimes from US and other countries.
Geng said cyber attacks are transnational, anonymous and deceptive with their source often difficult to identify.
Releasing irresponsible information will not help solve problems, he said and reiterated that China is a major victim of cyber attacks.
Statistics show that Chinese military end users connected to the Internet frequently come under cyber attack from abroad.
In these cases, source IP addresses suggest that the majority of them come from the US, Geng said, adding, "But we do not point fingers at the United States based on the above-mentioned findings, and every country should deal with cyber security in a professional and responsible manner."
To address criticism from foreign statesmen and media outlets about Chinese hacking, the Chinese side would like to resolve the issues through joint law enforcement and consultations with other countries, he said.
According to the spokesman, the Chinese Ministry of Public Security has assisted more than 50 countries and regions in investigating some 1,100 cases of cyber crime since 2004.
China has established bilateral law enforcement cooperation with over 30 nations and regions, including the United States, Britain, Germany and Russia, he said.
Lodging one-sided media accusations will not help solve problems, but only jeopardise existing cooperation, he said.
Asked whether China took up allegations of cyber attacks from US with Washington Chinese Foreign Ministry spokesman, Hong Lei told a media briefing that China maintained communication on the relevant issue and called for international cooperation to deal with it.
"Groundless speculation and accusation on the cyber attack is neither professional nor responsible. It is counter productive as well. China is firmly against cyber attacks," he said and called for international code of conduct on such attacks.
China and Russia have already put forward draft proposals in the UN in this regard, he said.
Chinese analysts, meanwhile, criticised the allegations.
Jin Canrong, an American studies expert with Renmin University, said the real motive behind the US hacking accusation is to seek an upper hand in Sino-US relations.
It signalled that the US is looking for fresh topics to criticise China in an effort to achieve dominance, Jin told Xinhua.
"Our analysis has led us to conclude that APT1 (Advanced Persistent Threat) is likely government-sponsored and one of the most persistent of China's cyber threat actors. We believe that APT1 is able to wage such a long-running and extensive cyber espionage campaign in large part because it receives direct government support," said the executive summary of the 60-page report.
Mandiant said it believes the group behind the hacking is Unit 61398, within a wing of the People's Liberation Army. It said it has observed hacking attempts against nearly 150 victims over seven years. Hundreds of terabytes of data were involved, it said.
A series of cyber attacks on America's most high-profile media outlets, reported earlier this month by The New York Times and the Wall Street Journal, as well as on Twitter and others, have revived concerns over Chinese hackers.
The New York Times said hackers stole corporate passwords and accessed the personal computers of 53 employees after the newspaper published a report on the family fortune of China's Premier Wen Jiabao.
Beijing: China's Defence Ministry Wednesday denounced as "groundless" the accusation by a US security firm that a secretive PLA unit is engaged in sophisticated cyber espionage around the world, saying the allegation lacked technical proof and legal basis.
First Published: Wednesday, February 20, 2013, 17:39