Bruce Schneier has claimed that China and Russia have laid hands on the intelligence documents leaked by the NSA whistleblower Edward Snowden, in a further twist to a controversial story run by the Sunday Times last weekend.

Journalists at the British paper had written that the Asian powers had "cracked the top-secret cache of files", citing a number of anonymous sources from Downing Street, the Home Office and the national intelligence services.

In the wake of its publication security experts were quick to pull apart the story, with Glenn Greenwald, the former Guardian journalist who broke the Snowden story, arguing that the piece "offers zero evidence or confirmation for any of its claims".

Whilst Schneier agreed that the article was "terrible", he argued that it is likely that the Snowden documents had fallen into the hands of US rivals despite the whistleblower’s efforts to protect them.

"It’s been open season on the computers of the journalists Snowden shared documents with since this story broke in July 2013," Schneier said, writing in Wired.

"And while they have been taking extraordinary pains to secure those computers, it’s almost certainly not enough to keep out the world’s intelligence services."

He added that the Snowden files may also have been stolen directly from the American and British security agencies, citing decades of attacks on organisations such as the US signals body the NSA.

"In general, it’s far easier to attack a network than it is to defend the same network," he said. "This isn’t a statement about willpower or budget; it’s how computer and network security work today."

His comments follow only a week after it was revealed the US government’s Office of Personnel Management was attacked, leaking the social security numbers of the country’s civil service staff.

They also come amid important decisions regarding surveillance on both sides of the Atlantic, with the US choosing to curb powers by allowing a clause enabling bulk phone metadata collection to lapse, whilst the British government prepares to revive the so-called Snooper’s Charter.