A supermarket cyber-attack has hit refrigerators and freezers in dozens of stores across seven European countries.

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

Sabcobel, a Belgian company that manufactures some of the affected refrigerators, said the units’ evaporators were switched to defrost mode. This caused the units to warm up. The company believes the same method was used in last month’s incident that hit hundreds of French supermarkets.

Local media reported at the time that millions of euros worth of food had to be thrown away in October. In the latest incident, freezers in several shops across Europe reportedly reached as high as 50C (122F).

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

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

Most supermarkets across Europe are linked to the internet. Maintenance and troubleshooting can also be done remotely. “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,” Moelans added.

It is unclear who is behind the latest apparent supermarket cyber-attack. Meanwhile, authorities in the US are investigating what caused refrigeration malfunctions at a number of American military bases in August. They are working with French officials to examine whether the incidents could be linked.

Both Belgium and Sweden’s national cybersecurity agencies said they were monitoring the incident. The UK’s National Cyber Security Centre said it was working with international partners and industry to “fully understand details of an incident”. No incidents have been reported in the UK.

The financial impact is already visible. In Flanders, northern Belgium, a Delhaize branch in Hoeilaart told the news website Het Laatste Nieuws that it had lost €100,000 (£83,500) worth of produce. The manager said the estimate did not include further losses that would result from closing the shop.

For now, the supermarket cyber-attack remains under investigation by national agencies and international partners, with no responsible party identified.

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