"This guidance was also reissued on Friday following the emergence of this issue".
If you're facing a ransom demand and locked out of your files, law enforcement and cybersecurity experts discourage paying ransoms because it gives incentives to hackers and pays for their future attacks.
A message will appear onscreen with a ransom demand, countdown timer and bitcoin wallet to pay funds into. Instead, most of the attention has been focused on the NSA exploit used in the attack, the actual threat posed to victims and vital systems, and the sheer magnitude of the event.
Ms Rudd said the National Crime Agency (NCA) and the National Cyber Security Centre (NCSC) were now part of an "international manhunt" to find the perpetrators.
USA package delivery giant FedEx, Spanish telecoms giant Telefonica and Germany's Deutsche Bahn rail network were among those hit in the attacks, which demanded money to allow users to unblock their computers.
Marcus warned more attacks are possible. However, officials and security firms said the spread was starting to slow.
In China, "hundreds of thousands" of computers were affected, including petrol stations, cash machines and universities, according to Qihoo 360, one of China's largest providers of antivirus software. I don't believe it is to do with our preparedness.
The virus hit computers running older versions of Microsoft software that had not been recently updated.
"The recent attack is at an unprecedented level and will require a complex worldwide investigation to identify the culprits", the European police agency added.
Russian President Vladimir Putin said on Monday that intelligence services should beware of creating software that can later be used for malicious means. 'If they know where I live, they could do anything, ' he said. It operates by locking infected computers. Some have also been machines involved in manufacturing or hospital functions, hard to patch without disrupting operations. NHS cyber attack has been reported in 74 countries which include Ukraine, India, Taiwan, Japan and Spain.
In England, 48 National Health Service (NHS) trusts fell victim, as did 13 NHS bodies in Scotland. However, the biggest impact was seen on the healthcare industry in United Kingdom, with appointments being cancelled and patient schedules being impacted across hospitals and clinics.
The attack came after warnings of NHS vulnerability, with cyber security allegedly neglected despite a series of attempted hacks.
However, Bossert warned that following the patching advice from Microsoft and the Federal Bureau of Investigation should be a top priority to stop the spread of ransomware, which has hit a number of large-profile companies, including FedEx.
It was not immediately clear whether those services were suspended due to attacks, or for emergency patching to prevent infection.
The best way to protect a computer system or all your information against ransomware attacks, is to back all the data up offline and in a separate system.
"We haven't fully dodged this bullet at all until we're patched against the vulnerability itself", Kalember said.
Elsewhere in Asia, the impact seems to have been more limited.
Hospitals were crippled on Friday following widespread "ransomware" attacks.
However, Wainwright said Europol was working on the basis that the cyber-attack was carried out by criminals rather than terrorists, but noted that "remarkably few" payments had been made so far.
Hackers bait users to click on infected email links, open infected attachments or take advantage of outdated and vulnerable systems.