Hackers raised the temperature of refrigerators and freezers at hundreds of French supermarkets to as high as 50 degrees overnight, causing fires and spoiling food.
The spoilage is estimated to be tens of millions of Euros.
Félix Aimé, a senior cyber threat intelligence analyst at Sekoia Threat Detection and Research, said Spain, Portugal, Poland, Germany and Belgium had also been affected.
Carrefour said 80 of its supermarkets were hit, while Monoprix, which operates about 490 stores in France, said five per cent of its stores were affected.
Les Mousquetaires, owner of retailer Intermarché, said fridges at around 150 of its stores were heated up to 50 C for six hours overnight. A spokesperson said all affected food had been discarded to eliminate health risks.
Coopérative U’s chief executive officer (CEO) Dominique Schelcher said his supermarket group had also been targeted.
Intermarché CEO Thierry Cotillard told BFM TV the "unprecedented" attack would represent losses amounting to "tens of millions of euros nationwide in a single day."
The attacks resemble disruptions reported at about a dozen U.S. military commissaries in late August that led to food losses after fridges were affected.
Dutch retailer Ahold Delhaize, which operates the Netherlands's largest supermarket chain Albert Heijn and has major operations in the U.S., said it was dealing with a "security issue" on its network and had taken several systems offline as a precaution.
A message on the retailer's smartphone app said it was unable to deliver groceries because of a "cybersecurity incident."
Online orders account for about 10 per cent of Albert Heijn sales. Physical stores remained open, while Dutch news agency ANP reported that rival retailers had seen a surge in delivery orders.
