The incident comes just weeks after hundreds of retail stores were targeted in a similar high-profile cyber assault across France.

The latest wave of attacks saw temperatures in supermarket refrigeration units after hackers remotely tampered with controls and exploited the defrost mode of the cooling hardware.

Retail chains affected include Ica and Coop in Sweden, along with Ahold Delhaize and Carrefour in Belgium. Store managers reported that hot air was blown directly into the units, ruining entire inventories of chilled and frozen goods.

“We can’t adjust the temperatures, we can’t change them. Hot air is blowing into the freezers. Everything is ruined,” said Rickard Nilsson, head of an Ica shop in Sjöbo, southern Sweden.

Stephan Moelans, chief executive of Belgian refrigeration company Sabcobel, noted that technicians had worked through the night to disconnect affected installations from the grid after hackers targeted the defrost mode to cause rapid temperature surges.

While it remains unclear who is officially behind the attack, Belgium’s Centre for Cybersecurity has upgraded the incident to a national status, mobilising intelligence and security services to investigate.

Experts warn that the scale of the attacks highlights severe vulnerabilities in industrial hardware and operational technology (OT) connected to the internet.

Robert Lee, chief executive of cybersecurity company Dragos, pointed out that large language models are making it easier for malicious actors to access the expertise needed to target hundreds of sites simultaneously. “We’ve never had hundreds of supermarkets at once,” Lee noted.