These coordinated hacks also affected supermarkets in Belgium and Sweden two days ago, after French supermarkets last month.
Life-saving blood products, including plasma bags, were targeted in several French regions.
After supermarket refrigerators, hackers therefore targeted a contractor of the French Blood Establishment.
The alarms made it possible to intervene in time. No product was lost, the establishment says.
The alert was forwarded to EFS headquarters. The company reacted quickly and took the necessary measures.
The attack is unprecedented, even though no losses are to be deplored.
"It's supposed to be secure, it's blood after all, it's something important,"one of them said.
Refrigerators are easy targets, according to an expert.