More than 50 Norwegian oil and energy companies have been hacked by unknown attackers, according to government security authorities.

A further 250 firms have been advised by the Norwegian government that they ought to check their networks and systems for evidence of a breach, The Local reports.

State-owned Statoil, Norway's largest petro company, appears to be the main target of what's described as the country's biggest ever hack attack. Statoil is a major contributor to the Norwegian government's coffers, and as such - unlike most major oil and gas companies, perhaps - its revenues mainly go to fuel the Scandinavian social miracle rather than funnelling wealth to the usual suspects.

National Security Authority Norway (Nasjonal Sikkerhetsmyndighet – NSM) passed on the warnings after it was tipped off regarding imminent attacks by "international contacts".

The methods and motives of the unknown perpetrators remain unclear.

Attacks of this type in Norway have been seen before. Three years ago, at least ten oil, gas and defence sector firms in in Norway were hacked via targeted spear-phishing emails. Unidentified hackers made off with industrial drawings, contracts and login credentials. ®