Chinese state media on Friday condemned as "irresponsible" suggestions the country was behind a massive global cyber spying campaign uncovered this week by a US computer security firm.

California-based McAfee described the sophisticated hacking effort as a "five-year targeted operation by one specific actor", without naming a country, but analysts and reports said China was the likely culprit.

The People's Daily, the mouthpiece of the Communist Party, said the claim that China hacked victims including the United States, United Nations, defence contractors and the International Olympic Committee "does not hold water".

"It is irresponsible to link China to Internet hackers," the newspaper added, in China's first response to the claims. McAfee said it had discovered the hacking campaign dubbed "Operation Shady RAT" by gaining access to a command and control server in a Western country used by the intruders and examining its logs.

Attacks on Asian and Western national Olympic committees, the International Olympic Committee and the World Anti-Doping Agency occurred immediately before and after the 2008 Beijing Olympics, McAfee said.

This was "particularly intriguing and potentially pointed a finger at a state actor behind the intrusions, because there is likely no commercial benefit to be earned from such hacks," it added. The victims also included the governments of Canada, India, South Korea, Taiwan, the United States and Vietnam, McAfee said.

The attacks involved sending infected emails to employees of the targeted companies. When opened, the emails implanted malware and established a backdoor communication channel to the command and control server.

China has been accused by the United States, Canada and other nations of spearheading online attacks on government agencies as well as companies, although the Beijing government has always denied this.

In June, Internet giant Google said a cyber-spying campaign originating in China had targeted Gmail accounts of senior US officials, military personnel, journalists and Chinese political activists. The computers of Australia's Prime Minister, Foreign and Defence Ministers were all suspected of being hacked in March, with China under suspicion.

Security experts cited by media at the time said they believed the hackers may have been looking for clues on government attitudes to major resource projects.