Greenwald collaborated with the news agency that first reported the details, working off records leaked to him by former U.S. National Security Agency contractor Edward Snowden, he said in an interview with Carol Off, host of CBC Radio's As It Happens.
And there may be more to come.
In the interview to air at 6:30 p.m. Monday on CBC Radio, Greenwald said he "absolutely" has "a lot more" to report on spying by Canada.
"There's a lot of other documents about Canadians spying on ordinary citizens, on allied governments, on the world, and their co-operation with the United States government, and the nature of that co-operation that I think most Canadian citizens will find quite surprising, if not shocking, because it's all done in secret and Canadians are not aware of it," Greenwald said.
The original report on Globo television alleges the Communications Security Establishment Canada, or CSEC, was using metadata from phone calls and emails to track the communications of Brazil's Energy and Mines Ministry.
'Express satisfaction in the results'
CSEC, as well as the offices of Canadian Prime Minister Stephen Harper and National Defence Minister Rob Nicholson, refused to comment on foreign intelligence gathering activities.
Asked if the document on which he reported Sunday showed where Canada benefited from the alleged espionage, Greenwald said he can't talk about documents he hasn't published yet.
"But obviously Canada is not expending enormous amounts of money to create a spying system that doesn't produce any valuable secrets. And ... even in this document, they express satisfaction in the results of their efforts and so I think it's fair to infer even just from this document that they reaped benefits from this."
Asked whether he has documents discussing specific companies, Greenwald again declined to comment.
"I'm just not going to talk about what's coming until it's ready," he told Off.
Greenwald said the document was in the NSA's possession because it had been presented at a signals development conference held by the Five Eyes, the name given to five allied countries that collaborate on foreign intelligence: Australia, Canada, New Zealand, the U.K. and the U.S.
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