Hackers have forced the temperature of many French supermarket fridges up to 50C overnight, in an “unprecedented” cyber-attack affecting several hundred stores across the country, with fires and food losses reported.

The Paris prosecutor’s office said on Monday ⁠the large-scale attack was “affecting connected refrigerators ⁠in several ​major food retailers across France”. Reported damage included “food losses and fires”, it added.

The prime minister, Sébastien Lecornu, instructed France’s national cybersecurity agency ANSSI to investigate, ⁠a person in his office said.

France “was coordinating with its European counterparts, as other countries may also be affected”, while also investigating whether any other French ⁠firms were at risk, they said.

Les Mousquetaires, which owns retailer Intermarché, said about 150 of its stores had been ​hit, with fridges heated up to 50C for six hours. ‌It had thrown all the food away to avoid any health risks, a spokesperson said.

Dominique Schelcher, chief executive of Coopérative ‌U, said his supermarkets had also been hit by the attack. “Targeting equipment essential to the preservation of fresh products and to the food supply of the French people is of extreme gravity and is unprecedented,” he wrote on X.

Several other supermarket chains, including Carrefour, Monoprix and Auchan, did not respond to requests for comment. According to BFM TV, France’s largest supermarket chain E Leclerc was also affected, with hackers “managing to remotely trigger the forced defrosting of the refrigeration systems in numerous stores”. E Leclerc did not respond to a request for comment.

The attack may not have been confined to France. The Dutch supermarket company ‌Ahold Delhaize said it was also dealing with a “security issue” in its network, and had taken several systems offline to protect them.

Stores of its Albert Heijn chain, ​the largest supermarket chain in the Netherlands, which also has several stores in Belgium, remained open in both countries. But its online app and delivery system were down, while electronic price tags often displayed the wrong information.

It was not clear if there was any link between the French supermarket attack and the ⁠problems flagged by Ahold Delhaize.

Delhaize supermarkets, also part of Ahold Delhaize but operating ​in Belgium and Luxembourg, were ​also affected by the security issue, ​Belgian media reported.

The source close to Lecornu said ANSSI had identified a vulnerability ​in software supplied by ‌the Danish company Danfoss.

Danfoss ​said it was “aware ​of incidents in France affecting a limited number of refrigeration management systems”.

The affected units “were running outdated firmware”, Danfoss said, adding that it had “long advised customers to keep supported systems updated with the latest firmware and to migrate legacy systems to current-generation solutions”.

The incident comes against the background of growing concern over the potential havoc that can be caused in Europe in all sectors by cyber-attacks by malicious actors.

The French president, Emmanuel Macron, a strong supporter of Ukraine in its fight against the Russian invasion, last month ordered measures to protect France’s critical infrastructure from Russian “hybrid attacks”.