The attacks come two months after another global ransomware assault, known as Wannacry, which caused major problems for the UK’s National Health Service.
Veteran security expert Chris Wysopal from Veracode said the malware seemed to be spreading via some of the same Windows code loopholes exploited by Wannacry. Many firms did not patch those holes because Wannacry was tackled so quickly, he added.
Those being caught out were also industrial firms that often struggled to apply software patches quickly.
“These organisations typically have a challenge patching all of their machines because so many systems cannot have down time,” he said. “Airports also have this challenge.”
Copies of the virus have been submitted to online testing systems that check if security software, particularly anti-virus systems, were able to spot and stop it.
“Only two vendors were able to detect it so many systems are defenceless if they are unpatched and relying on anti-virus,” he said.
Ukraine seems to have been particularly badly hit this time round.
Reports suggest that the Kiev metro system has stopped accepting payment cards while several chains of petrol stations have suspended operations.
Ukraine’s deputy prime minister has tweeted a picture appearing to show government systems have been affected.
His caption reads: “Ta-daaa! Network is down at the Cabinet of Minister’s secretariat.”