A cyber-attack has caused supermarket refrigerators and freezers to warm up across seven European countries, with temperatures reportedly reaching 50°C in several shops and one Belgian branch estimating €100,000 (£83,500) in spoiled produce.

Sabcobel, a Belgian manufacturer that operates Delhaize’s refrigeration systems, said evaporators had been switched to defrost mode. Around 40 Delhaize supermarkets in Belgium and Luxembourg were affected, alongside shops in Sweden, Ireland, the Netherlands, Estonia and Finland.

The method is believed to resemble that used against hundreds of French supermarkets in early October, when food worth millions of euros reportedly had to be discarded. Who carried out the latest attack remains unknown.

Sabcobel chief executive Stephan Moelans said on Monday that teams had worked through the night and morning to disconnect affected units. The company had been addressing the vulnerability since the French attack, but the equipment required physical modifications, not merely software updates.

Internet connections allow remote maintenance and troubleshooting at most European supermarkets. Moelans advocated secure connections, saying most customers had switched after the French incident. The immediate disconnections and longer-term modifications underline the distinction between containing the attack and remedying the vulnerability.

At Delhaize’s Hoeilaart branch in Flanders, the manager said the €100,000 estimate excluded further losses from closing. Carrefour said 15 Belgian stores were affected but immediate measures kept all shops open. Colruyt Group reported attacks at five franchised Spar shops. Ikea confirmed affected refrigeration at Mons, while saying it could not rule out additional locations.

In Sweden, ICA said a small number of stores outside its central network were affected and receiving support. Its Sjöbo branch said hackers had set temperatures to 50 degrees; it reopened after closing earlier. Coop said seven of its 800 Swedish stores were affected, but the situation was contained and under control.

Ireland’s Musgrave Group confirmed disruption at 13 SuperValu supermarkets, limited to a specific refrigerator model. Manufacturer Danfoss said at least 17 Dutch companies were attacked overnight, including butchers and neighbourhood shops. Finland’s Kesko was investigating malfunctions at some K-stores. An Estonian Selver supermarket was affected, with reports of other companies experiencing problems.

Belgian and Swedish cyber-security agencies were monitoring developments. Britain’s National Cyber Security Centre was working with international partners and industry to understand the incident; no UK incidents had been reported.

US authorities are also investigating August refrigeration malfunctions at several American military bases and working with French officials to examine possible links. Whether those incidents are connected remains unresolved.