At least 50 companies in Norway’s oil and gas industry have been hacked, reports claim.

A further 250 firms have also been warned by the nation’s prevention unit for cyber attack – National Security Authority (NSM) – as it revealed the news.

It is believed a virus has been spread via malware-infected emails sent to “selected individuals in large Norwegian companies”.

Kjetil Berg Veire, Head of information at the NSM has been quoted as saying: “I can confirm that the Norwegian National Security Authority has revealed a computer espionage operation especially targeted towards businesses within the oil and gas sector, the energy sector and military industry.”

Reports claim Statoil is one of the companies that have been warned of the attack by NSM. A spokesperson from the company was quoted as saying: “We have received a warning and are, as a matter of routine, checking our systems.”

Earlier this year security experts revealed European energy firms were spied on by a cyber gang.