French authorities say that fridges used in medical facilities to store blood for donations were impacted by recent cyber-attacks by unknown hackers.
The French Blood Establishment (EFS) said cold rooms storing blood were impacted by hackers, with temperatures set to rise - but staff intervened to protect blood supplies.
"No health impact has been identified and no loss of blood products is to be reported," the EFS said.
Up until now, only supermarkets were known to have been impacted by the hacks.
Meanwhile rumours have been circulating online about Russian hacktivist groups claiming they worked together on the waves of freezer hacks which have affected European supermarkets.
Noname057(16) and Z-Pentest Alliance reportedly posted on Telegram that they were responsible, bragging that they had "once again demonstrated a high level of skill and precision".
But their posts and channels have now been deleted and the claims are being met with some scepticism.
While Russian groups are not being ruled out, experts say Iranian hacktivists or nation state hackers - or even teenagers pulling pranks - could also be the culprits.
Cyber-security researchers at multiple firms are pouring over evidence gathered from so-called "honeypots" to provide clues as to who is behind the waves of freezer hacks.
Three separate cyber-security firms have deployed fake freezer software traps to monitor how hackers attempt to use them for attacks.
In cyber-security, a "honeypot" is a digital decoy - such as a fake computer network or file - deliberately set up to look like a vulnerable target to lure and trap hackers.
By monitoring these traps, security experts can safely study an attacker's methods without putting real systems at risk.
According to activity gathered after the first wave of cyber-attacks, the second wave which hit several European countries was highly targeted.
"The fact that all these fridge freezers were hit simultaneously suggests planning and coordination," says Ryan Dewhurst from Spanish cyber-security company Previdian.
The entry point to the affected freezer software products was not difficult to exploit as they were poorly protected, with known attack methods already floating around online.
But experts like Dewhurst say the hacker or hackers had to gather the information about the devices' public IP addresses to create a target list then take time to plan which methods to use and when to execute them.
"Given the reported timing of when the devices had their temperatures increased, which seems to have been overnight for maximum damage - this is further evidence that the attack was planned and co-ordinated," he said.
Another cyber firm which has deployed similar honeypot tech to lure the hackers into revealing their tactics is Strathclyde-based Lupovis.
It had honeypots which appeared to be located around the world, and started seeing activity 10 days before the second wave of cyber-attacks.
Intriguingly, the team saw hackers scanning and probing their fake freezer sites only in Europe.
"We saw none of our honeypots in places like Africa or South America targeted at all," said Lupovis founder Dr Xavier Bellekens.
"Even pots in Ukraine were left alone."
A third company - French cyber-defence firm Sekoia - also noticed scanning activity prior to the second wave of cyber-attacks, but said it could have been automatic scanning without malicious intent.
In a report to its customers, it said evidence suggested the nature of the attack aligned with activity of Russian hacktivists or the Russian government, which is being accused of carrying out so-called "hybrid warfare" cyber-attacks across Europe.
But Sekoia's research also points to Iranian regime hackers or hacktivists too.
"Iranian-aligned actors have an established record of targeting internet-exposed industrial control systems and previous incidents involved the same equipment in Israel and the US - both adversaries of Iran," the report said.
According to Sekoia, about 40 Israeli supermarkets running Danfoss controllers were compromised back in 2022.
Meanwhile in late August, freezers in at least six US military bases were forced into defrost mode, as in France. The controller models remain unconfirmed and investigations are ongoing.
In a now deleted post online, NoName and Z-Pentest Alliance claim to have targeted freezer software maker Danfoss since the start of 2026.
"To date, we have no technical evidence indicating the involvement of Russian-speaking groups," a Sekoia spokesperson told the BBC.
"Furthermore, as NoName057 is not known to effectively conduct operations beyond DDoS attacks and has a history of making false attributions, we remain sceptical of their alleged claim of responsibility."
Distributed denial of service (DDoS) attacks work by flooding a website or online service with internet traffic in an attempt to throw it offline, or otherwise make it inaccessible.
Authorities in several countries are actively investigating the hacks and warning supermarkets about potential future attacks.
But no formal attribution has been made.
None of the three cyber firms which have been gathering honey pot data are ruling out that it could be a teenager.
But with the degree of planning necessary the experts all agree it would have to be a well co-ordinated group - and if so, they would expect online bragging to surface soon.
Sekoia also said the possibility remains that all three waves could have been carried out by different and distinct groups or copycats.
