Hackers have used an email-borne virus to steal documents, industrial designs and users log-ins from numerous Norwegian power and defence companies.

The virus, delivered as an email attachment to selected individuals in oil and gas companies and arms manufacturers in the country, operates underneath anti-virus software, according to the Norwegian National Security Agency (NSM), "Updating the software and operating systems is essential, antivirus is not," it said.

NorCERT, NSM’s cyber crime division of NSM, was able to pin the attacks on a single source by analysing network traffic and the code of the virus. 

"All ten cases were revealed this year and there are some cases where computers have been effected for months," NSM spokesperson Kjetil Berg Veire told Information Age. "Norwegian police are currently investigating."

"We must assume that the actual number [of attacks] is much higher, but that many [companies] have not made contact with NorCERT (Norwegian Computer Emergency Response Team)," Viere wrote earlier this week.

Due to the hidden nature of the virus, Viere said that it was "likely that industrial secrets from various companies have been stolen and sent digitally out of the country."

The NSM said that this was the first time that Norway had been the target of "comprehensive and wide computer espionage attacks."