Shops in seven countries reported problems with their fridges on Monday, the Guardian reports. They were in Belgium, Estonia, Finland, Ireland, Luxembourg, the Netherlands and Sweden. Temperatures in some fridges and freezers rose as high as 50C (122F), the Guardian and the BBC report.

About 40 Delhaize supermarkets in Belgium and Luxembourg were affected, the BBC reports. Smaller numbers of shops were hit in the other countries, the BBC says.

Stephan Moelans runs Sabcobel, which operates Delhaize's fridge systems. He called the incident a cyber-attack, the BBC reports, citing the Belga news agency. He said the units' evaporators were switched to defrost mode, causing them to warm up. His company spent the night and morning disconnecting the affected units from the network, he said.

Moelans said the units needed physical changes, not just software updates, to protect them, the BBC reports.

Several companies said they had been hacked, the Guardian reports. A Carrefour spokesperson, Mich Vergauwen, said: "It's a cyber-attack, there is no other reason." Carrefour said about 15 of its Belgian shops were affected, the BBC and the Guardian report.

The EU food and agriculture commissioner, Christophe Hansen, called the attacks "a deliberate attempt to disrupt our food supply chain and undermine consumers' confidence in it," the Guardian reports. No one has publicly been identified as responsible in the cited reports.

Last month, hackers seized control of cooling units in as many as 700 French supermarkets, the Guardian reports. That attack caused fires and food losses estimated in the tens of millions of euros, the Guardian says.

Cyber agencies in Belgium and Sweden said they were watching the incident, the BBC reports. The UK's National Cyber Security Centre said no incidents had been reported in the UK, the BBC says.

What we know: Shops in seven countries reported fridge and freezer failures on Monday.
What we don't know: Who carried out the attack and how much food was lost overall.