Oil, gas and defence companies in Norway have been hit by a series of sophisticated hack attacks.
The National Security Agency said industrial secrets and information about contract negotiations had been stolen. It said at least 10 firms had been targeted.
Norway is the latest in a growing list of nations that have lost secrets and intellectual property to cyber thieves.
The BBC reports the attackers won access to corporate networks using customised emails with viruses attached which did not trigger anti-malware detection systems.
The NSM said the email messages were sent to specific individuals in the target firms and were carefully crafted to look like they came from legitimate sources.
The BBC reports many of the emails were sent while the companies were in the middle of negotiations over big contracts.
The NSM said user names, passwords, industrial drawings, contracts and documents had been stolen.
In a statement, the NSM said this was the first time that Norway has revealed extensive and wide computer espionage attacks.