The ransomware worm that stopped vehicle factories, hospitals, shops and schools over the weekend worldwide, with Asia having escaped the worst so far, could wreak fresh havoc on Monday when employees log back on, cyber security experts warned.
The hunt was on for the culprits behind the assault, which was being described as the biggest-ever cyber ransom attack.
After taking computers over, the virus displayed messages demanding a payment of $300 in virtual currency Bitcoin to unlock files and return them to the user.
The ransomware, called WannaCry, locks down files on an infected computer and asks the computer's administrator to pay in order to regain control of them.
"I can not put my hand on my heart and say that means we are 100 per cent cyber secure", he said.
"Very few banks, if any in Europe, have been affected by this and that's because they've learned through painful experience about being the number one target for cybercrime, the value of having a proper strategy in place", Weinwright said.
Security experts said the attack appeared to be caused by a self-replicating piece of software that enters companies when employees click on email attachments, then spreads quickly internally from computer to computer when employees share documents.
It exploited a vulnerability in the Windows operating system believed to have been developed by the National Security Agency, which became public last month.
Ciaran Martin, chief executive of the National Cyber Security Centre (NCSC), warned there could be a fresh wave of victims on Monday. It is too early to tell.
In the United States, FedEx acknowledged it had been hit by malware and was "implementing remediation steps as quickly as possible".
It is understood its plant in Sunderland is not due to have another production shift until Sunday night.
The Federal government has confirmed an worldwide cyber attack that hit at least 74 countries has reached Australia, with one local business "likely" to have been affected by malicious ransomware.
British Prime Minister Theresa May said there was no evidence patient data had been compromised and added that the attack had not specifically targeted the National Health Service.
In Germany, the federal railway operator said electronic boards had been disrupted. Universities in Greece and Italy also were hit.
The 22-year-old researcher known as "MalwareTech", who wanted to remain anonymous, said he spotted a hidden web address in the "WannaCry" code and made it official by registering its domain name.
"We could potentially see copycats mimic the delivery or exploit method they used", he said. Hackers said they stole the tools from the NSA and dumped them on the internet.
While the researcher is being lauded online for helping to prevent a more widespread outbreak, MalwareTech doesn't consider themselves a hero. G7 finance ministers meeting in Italy discussed the attacks and were expected to commit to stepping up global cooperation against a growing threat to their economies.
Also badly hit was Britain's National Health Service, which declared a "major incident" after the attack, which forced some hospitals to divert ambulances and scrap operations.
Coming from an emergency Cobra meeting, Rudd said that "there's always more" to be done to protect against these kinds of computer viruses.
A spokeswoman said the company was "doing what is needed to counter this attack".