Dozens of supermarkets across six European countries have been hit by a suspected cyber-attack affecting their refrigerators and freezers.

Around 40 Delhaize supermarkets in Belgium and Luxembourg were affected, while a smaller number of shops were hit in Sweden, Ireland, the Netherlands and Estonia.

Sabcobel, a Belgian company that manufactures some of the affected refrigerators, said the units’ evaporators were switched to defrost mode causing them to warm up, in what is believed to be the same method used in last month’s incident that hit hundreds of French supermarkets.

Millions of euros worth of food has had to be thrown away, according to local media reports.

Stephan Moelans, the CEO of Sabcobel, which operates Delhaize’s systems, told the Belga news agency that the incident was a cyber-attack and that the company had been “working all night and morning to disconnect the affected units from the network”.

He said since the French attack in early October, the company had been working to “protect our customers fridges against this vulnerability” but that the units needed physical modifications, not just software updates.

“The simplest solution is to manage the fridges over a secure internet connection. Most of our customers switched to that after the attack in France,” he added.

It is unclear who is behind the apparent attack.

The temperature of freezers in several shops across Europe reportedly rose to as high as 50C (122F).

Both Belgium and Sweden’s national cyber-security agencies said they were monitoring the incident.

A Delhaize branch in Hoeilaart, in Flanders, Beligum, told Het Laatste Nieuws it had lost €100,000 (£83,500) worth of produce.

The manager said that estimate did not even take into account further losses that would result from closing the shop.

Carrefour, a French-owned supermarket, said the incident had only affected 15 of its Belgian stores, adding that measures had been taken immediately to ensure all shops remained open.

A spokesperson for Colruyt Group, which operates Spar stores in Belgium under a franchise system, told Reuters news agency five shops had their fridge systems attacked.