Dutch supermarket group Ahold Delhaize had dozens of Delhaize stores affected in Belgium and Luxembourg, CNBC reports. The company said food had to be thrown away and that stores were now fully operating again, CNBC says.

Carrefour said 15 of its stores in Belgium were attacked, and Intermarché said 15 of its 153 stores there were affected, CNBC reports. Colruyt Group said five of its Spar stores in Belgium were targeted, according to Reuters, CNBC says.

“In most cases, the security measures in place made it possible to quickly contain the attack,” an Intermarché spokesperson said, CNBC reports.

Retailers in Belgium, Estonia, Finland, Ireland, Luxembourg, the Netherlands and Sweden reported problems with their refrigeration on Monday, The Guardian reports. Similar attacks hit France last month, the paper says.

The UK's National Cyber Security Centre said it was working with affected companies but that the national impact was minimal, The Guardian reports. “At the moment, the impact is minimal,” said Paul Chichester, its director of operations.

Experts said attacks on decoy fridge controls, placed online to lure hackers, showed features similar to operations linked to Russia, The Guardian reports.

The attack on French supermarket fridges last month involved older technology connected to the internet with default passwords, The Guardian says.

IKEA said a cyber incident hit fridges and freezers at its store in Mons, Belgium, CNBC reports. The store stayed open, CNBC says.

What we know: Hackers raised fridge temperatures at stores in several countries, and food was thrown away.
What we don't: Who is behind the attacks. No group has been named as responsible in the cited reports.