Someone Hacked Tons of French Supermarket Refrigerators and Set Them to Defrost. It’s Clever—and Alarming.

Here’s what you’ll learn when you read this story:

• Hackers seized control of refrigeration systems at roughly 700 French supermarkets last week, cranking temperatures as high as 50°C (122°F) and spoiling mountains of food.
• Security experts say the compromised controllers sat on the public internet with no VPN and critical vulnerabilities.
• Supermarket refrigeration is an energy and emissions hog, so researchers are working to turn these systems into “cold batteries” that support the grid, cut costs, and still keep your snacks frozen.

On Monday, October 12, bleary-eyed workers pulling the morning shift at hundreds of supermarkets across France were met with a shocking, foul-smelling surprise. Overnight, hackers compromised internet-connected controllers operating on software provided by the Danish company Danfoss, and set thousands of fridges to “defrost,” sending temperatures inside the units soaring to as high as 50 degrees Celsius (122°F). In some cases, the hack sparked small fires in the refrigerators.

“When I opened the freezers, there was no more cold — just hot air coming out,” Cyril Scheubel, a manager at an Intermarché supermarket outside of Dijon told NPR. “All of our computer data is very well-protected…these hackers hit the only vulnerable point of our stores.”

Ars Technica reports that all three controllers targeted in the attack—Danfoss (Denmark), Dixell (Italy), and Copeland (U.S)—contained critical vulnerabilities that allow hackers full system rights, as if they were administrators. Remarkably, the controllers sat on the public internet with no virtual private network (VPN) shielding remote access. The U.S.-based Copeland company also says the devices impacted were “a discontinued, end-of-life generation of controllers.”

Whatever the cybersecurity lapses, the result was likely millions of dollars’ worth of spoiled food, and the search is on for the culprits behind the attack. However, this strange story raises another question: Why were these refrigerators on the internet in the first place?

Travel to any supermarket in the U.S., and you’ll likely witness rows and rows of freezers and refrigerators continually chilling or freezing, well, pretty much everything—and those systems use a lot of energy in aggregate. In 2015, the Environmental Protection Agency’s National Center for Environmental Economics reported that refrigeration consumed 40 to 60 percent of the energy in a typical U.S. supermarket—enough, collectively, to account for up to three percent of all commercial building energy use in the country. Worse, the hydrofluorocarbons (HFCs) inside them are potent greenhouse gases in their own right, more than doubling these systems’ climate impact.

Naturally, with that much electricity on the line, supermarkets want their refrigeration running as efficiently as possible. The key reason, at least in the case of France, is that internet controllers allowed technicians to track cooling levels without having to be physically at the store. However, researchers in recent years have explored even grander ambitions for connecting these refrigerators online.

In 2018, for example, a pilot project in northern Finland tested the concept of demand response, where supermarket fridges could be cut off from power for up to 30 minutes without damaging food or the systems themselves. In a way, these big cold boxes became a kind of battery that would chill food when demand was low and then disconnect from power when demand was high. Part of this project was in preparation for a renewable power system that might provide energy during the day but less energy at night. The researchers found that while regular grocery stores consumed 600 kWh/m2, energy-efficient stores topped out at only 240 kWh/m2, which amounted to roughly $200,000 in savings per year.

The following year, U.K. supermarket chain Tesco partnered with the University of Lincoln to test a similar system, timing the fridges’ defrost cycles to match power availability on the national grid. The appeal is that refrigeration accounts for more than 14 percent of electricity demand in the U.K. at any given moment, and roughly a third of a typical grocer’s energy costs. Tesco alone has some 112,000 refrigeration systems under central software control, so adjusting them in unison has a significant effect on the national grid.

Because the thermal mass of a loaded refrigerated case stores cold like a battery, it can safely coast without power for tens of minutes, allowing supermarkets to chill hard when energy is cheap and pause when it isn’t. However, using refrigeration as grid storage requires precise control to avoid two critical limitations. First, cutting power while a case recovers from its daily defrost cycle severely delays its return to temperature. Second, restarting thousands of compressors simultaneously can cause massive electrical surges on the grid.

Despite these challenges, supermarkets are actively grappling with how to lower their greenhouse gas emissions and electricity costs. A 2025 report by the Environmental Investigation Agency recommended that natural refrigerants can help keep things cool, save money, and avoid HFC pollution. According to the report, Carrefour, one of the chains hit by the hack, spent nearly $90 million on low-GWP refrigeration technology in 2022. The investment now returns roughly $30 million a year and cuts some 67,000 tonnes of carbon dioxide annually.

The connectivity that makes a supermarket’s freezers useful to the grid is also what allowed hackers to switch thousands of them to “defrost.” Advances in supermarket refrigeration could both prop up the grid and drastically cut energy use and greenhouse gas emissions. But the near-term challenge is simpler: keeping those fridges—and the internet-connected gadgets that control them—out of the wrong hands.