The US National Security Agency has reportedly implanted software in nearly 100,000 computers around the world - but not in the United States - that allows the US to conduct surveillance.
Citing NSA documents, computer experts and US officials, The New York Times said secret technology using radio waves was being used to gain access to computers that other countries have tried to protect from spying or cyberattacks. The software network could also create a digital highway for launching cyberattacks, the newspaper reported.
The newspaper said the technology, used by the agency for several years, relies on radio waves that can be transmitted from tiny circuit boards and USB cards inserted covertly into the computers. The NSA calls the effort an "active defence" and has reportedly used the technology to monitor units of the People's Liberation Army, the Russian military, drug cartels, trade institutions inside the European Union, and US partners against terrorism like Saudi Arabia, India and Pakistan.
Among the most frequent targets has apparently been the PLA, which has been accused of launching regular attacks on American industrial and military targets, often to steal secrets or intellectual property.
When Chinese attackers have placed similar software on computer systems of US companies or government agencies, American officials have protested.
The NSA said the technology had not been used in computers in the US.
"NSA's activities are focused and specifically deployed against - and only against - valid foreign intelligence targets in response to intelligence requirements," Vanee Vines, an agency spokeswoman, said.
"We do not use foreign intelligence capabilities to steal the trade secrets of foreign companies on behalf of - or give intelligence we collect to - US companies to enhance their international competitiveness or increase their bottom line."
Parts of the programme have been disclosed in documents leaked by Edward Snowden, the former NSA systems analyst.
A Dutch newspaper published a map showing where the US had inserted spy software, while the German magazine Der Spiegel published information about the NSA's hardware products that could secretly transmit and receive signals from computers.
Hong Lei of the Foreign Ministry in Beijing said the US "on one hand has been playing up the cyberthreats from other countries, and on the other hand has been implementing cybersurveillance endangering the sovereignty, security and public privacy of other countries".
He urged the US to "work with the international community to create international regulations and build a peaceful, safe, open and co-operative cyberspace".
At New Delhi's Institute for Defence Studies and Analyses, cybersecurity expert Cherian Samuel said: "If it had been any other country doing this kind of thing, the US would have come down on them like a ton of bricks with punitive sanctions."