The attack has hit at least 150 countries since Friday and infected 200,000 machines, according to the European law enforcement agency Europol.
However, if your devices have been infected by WannaCry - the malware that has affected the NHS' computer system - the ransomware will lock your entire PC.
"We will get a decryption tool eventually, but for the moment, it's still a live threat and we're still in disaster recovery mode", Europol director Rob Wainwright told CNN on Sunday. And WannaCry threatens to create even more havoc on Monday when people return to work.
Cybersecurity experts have said the majority of the attacks targeted Russia, Ukraine and Taiwan.
"The global reach is unprecedented".
Oliver Gower, of the UK's National Crime Agency, added: "Cyber criminals may believe they are anonymous, but we will use all the tools at our disposal to bring them to justice".
It was restoring its advertising servers at dozens of theaters after the attack left the company unable to display trailers of upcoming movies.
Individuals and organisations were discouraged from paying the ransom, as it was not guaranteed that the access would be restored.More news: Macron names Edouard Philippe as new French prime minister
MalwareTech was hailed as an "accidental hero" after he helped prevent the virus from spreading further when he and another cyber security researcher stumbled upon a "kill switch" in the malware code.
Wanna Decryptor, also known as WannaCry or wcry, is the ransomware program behind the global cyber attack that affected the NHS.
Experts were urging organizations and companies to immediately update older Microsoft operating systems, such as Windows XP, with a patch released by Microsoft Corp.to limit vulnerability to a more powerful version of the malware - or to future versions that can't be stopped.
"Computers that had not been updated with the Microsoft patch were vulnerable to attack".
While this protected newer Windows systems and those with updates on, many computers remained unpatched. There could be other versions with enhanced destructive powers and with capabilities to invade computers using OS other than XP.
"The very nature of this particular malware, this sort of ransomware attack, is very potent because unlike more routine ones this one has used a sort of worm to exploit the operating system and bolted on a ransomware so that it spread incredibly quickly in hours not weeks or days", Wallace said. Hospitals, universities, manufacturers and government agencies in Britain, China, Russia, Germany and Spain have all been affected.
Tens of thousands of computer were "locked" - the screens displaying the telltale ransom demand. Victims who have already been affected are advised not to pay any "ransom" money as there is no guarantee that their files will be unlocked by the hackers.
Mr Fallon also claimed the Government had set aside more than £1.9bn in an effort to tackle cyber threats, of which a "large chunk" of £50m went to the NHS after an official security review highlighted hacks as a major threat.