Early this year, government officials acknowledged the federal Finance Department and Treasury Board, along with a Department of National Defense agency had been attacked by computers in China.
The departments turned off Internet access for most users in those departments, and they still have limited or no online access, the Canadian Broadcasting Corp. reported.
Meanwhile, Daniel Tobok, chief of the Digital Wyzdom cybersecurity company told the CBC the "very sophisticated and highly targeted" hacking attacks also affected at least seven major law firms in Toronto.
The crux of the attack appears to have been over a possible takeover of the Potash Corp. of Saskatchewan, at the time estimated to be worth $38 billion, the CBC said.
The law firms were all involved in sales negotiations, Tobok said.
Australian resource giant BHP Billiton was trying to acquire the company, which Beijing made no secret of opposing. China is one of the biggest importers of potash, used in agricultural fertilizers.
Canada's Conservative government earlier this year ruled out the sale of the corporation to foreign investors.