Speaking after a Cobra meeting on Saturday, Rudd admitted "there's always more" that can be done to protect against viruses.
That was the chilling prediction made yesterday by Ron Wainwright, the English-born head of the EU's crimefighting organisation Europol.
He said few banks in Europe had been affected, having learned through the "painful experience of being the number one target of cyber crime" the value of having the latest cyber security in place.
This particular attack used malicious emails to encrypt a computer's data and demand payment of hundreds of dollars to decode the data.
A fast-moving wave of cyberattacks swept the globe overnight, reportedly exploiting a flaw exposed in documents leaked from the US National Security Agency. Microsoft released a patch back in March, but many users and organizations had not updated their systems with the the fix. In an interview on ABC's "This Week", Clapper said the worry was "this ransomware attack will be even larger" as people return to their desks after the weekend.
By one security firm's count, the malware struck at least 74 countries, including the US, where its effects seemed muted.
Wainwright said Europol provided free downloads of decryption programs for most ransomware.
"There will be lessons to learn from what appears to be the biggest criminal cyber-attack in history", Interior minister Amber Rudd said.
Britain's national health service was hit hard, its hospitals forced to close wards and emergency rooms.
Trump meets Abbas, predicts 'very good chance' of peace with Israel
President Donald Trump welcomes Palestinian leader Mahmoud Abbas to the White House in Washington , Wednesday, May 3, 2017. Trump urged Palestinian leaders to condemn violence and terrorism against innocent people throughout the Middle East. "Mr.
Switching on will allow the HSE's central IT systems to update local machines with security patches and anti-virus capability, it said.
In addition to the UK's NHS, the WannaCrypt ransomware also hit Spain's Telefonica telco and other companies in Russia, Spain, Taiwan and Ukraine, according to the security firm Malwarebytes.
Gas stations: State-run media in China reported that some gas stations saw their digital payment systems shut down, forcing customers to bring cash.
British Prime Minister Theresa May said there was no evidence patient data had been compro-mised and added that the attack had not specifically targeted the National Health Service.
He advised the public to report any suspected ransomware attack to the Australian Cybercrime Online Reporting Network. Lieu said it is "deeply disturbing" the NSA likely wrote the original malware used to ransom computers.
Name SearchWatch Service' Patrick Ward, a 47-year-old sales director, said his heart operation, scheduled for Friday, was canceled at St. Bartholomew's Hospital in London.
According to Matthew Hickey, founder of the security firm Hacker House, the attack is not surprising, and it shows many organizations do not apply updates in a timely fashion.
'There have also been other reports made to our online cyber security network and the difficulty is of course there are literally hundres of instances of ransomware in Australia each week and so we are now seeking to confirm whether these are examples of the particular ransomware that has cause so much havoc for example in the United Kingdom'. As an additional "defense-in-depth" measure, keep up-to-date anti-malware software installed on your machines.