The FBI, the Times said, declined to comment on the operation.

Although the Canadian researchers said that most of the computers behind the spying were in China, the paper said, they cautioned against concluding that China's government was involved. The spying could be a non-state, for-profit operation, for example, or one run by private citizens in China known as "patriotic hackers."

"We're a bit more careful about it, knowing the nuance of what happens in the subterranean realms," Ronald J Deibert, a member of the research group and an associate professor of political science at Munk, was quoted as saying. "This could well be the CIA or the Russians. It's a murky realm that we're lifting the lid on."

A spokesman for the Chinese Consulate in New York, the paper said, dismissed the idea that China was involved. "These are old stories and they are nonsense," the spokesman, Wenqi Gao, said. "The Chinese government is opposed to and strictly forbids any cyber crime."