France's national blood service said three of its sites were affected. Universal Images Group via Getty Images

Hackers have come for blood.

France's national civilian blood service, the EFS, said its refrigerators were hit by a cyberattack on Monday that raised temperatures to "very high levels."

The attack hit three sites, affecting equipment storing blood samples and plasma used in transfusions, the EFS said in a press release. Hospitals often use frozen plasma for patients who are hemorrhaging or otherwise losing a lot of blood.

Hackers targeted a refrigeration equipment supplier, not the EFS itself, the release said. The EFS' monitoring and alarm systems identified the rising temperatures, and people responded to the attack before any samples or products were compromised or destroyed. Products at the facilities were "preventively transferred to other facilities," the EFS said.

The attackers aimed to raise temperatures from -22°F to 230°F, according to the French publication Le Canard enchaîné.…