In the USA, the virus attack was somthing that "for right now, we've got under control", said Tom Bossert, a homeland security adviser to President Donald Trump.
It says the latest virus exploits a flaw in Microsoft Windows identified by, and stolen from, U.S. intelligence.
Among the other victims is a Nissan manufacturing plant in Sunderland, northeast England, hundreds of hospitals and clinics in the British National Health Service, German rail operator Deutsche Bahn and worldwide shipper FedEx Corp.
According to security news blog SecurityAffairs, an estimated 200,000 computers across 150 countries had been attacked as of Monday.
The vulnerability in the Microsoft Windows software - exploited by "WannaCrypt" - crippled computers across the world, with hackers demanding hundreds of dollars from the users for them to regain control over their data. But these worm attacks became harder to pull off as computer owners and software makers shored up their defenses.
The code for the ransomware unleashed Friday remains freely available on the internet, experts said, so those behind the WannaCry attack - also known as WanaCryptor 2.0 and a variety of other names - could launch new strikes in coming days or weeks.
"Once it gets in and starts moving across the infrastructure, there is no way to stop it", said Adam Meyers, a researcher with cyber security firm CrowdStrike.
Hospitals across the United Kingdom have had systems knocked offline by the ransomware attack, with patient appointments cancelled and doctors and nurses resorting to pen and paper and NHS England declaring the cyberattack as a "major incident" - a total of 45 NHS organisations are now own to be affected.
Avast said the majority of the attacks targeted Russia, Ukraine and Taiwan.
The attack was spread through a vulnerability that was leaked last month in a trove of hacking tools believed to belong to the NSA.
"If people have already taken action and applied the software patch (issued by Microsoft), they need not worry". So much so, that the company has even released an update for those versions of Windows which are no longer supported. Kaspersky Lab said it had recorded incidents in 74 countries, mostly in Russian Federation, but noted that its visibility "may be limited and incomplete".
Experts fear the situation could further aggravate as a number of computers in India run on the older operating systems and have not been updated yet. Many canceled all routine procedures and asked patients not to come to the hospital unless it was an emergency. Power utilities also reported problems.
In Japan, several large manufacturers have been hit, reporter John Matthews tells NPR: "Companies including Hitachi have reported several of their systems going down, including computers at a hospital in eastern Japan".
"Otherwise they're literally fighting the problems of the present with tools from the past", Smith wrote.
IT Minister Prasad revealed that government had issued an advisory in March itself, informing administrators about the "software patch" in Microsoft which could be used against a possible attack. By choosing to implement the right updates, you can be hopeful of improved security and lesser chance of attack. Spanish telecom company Telefónica was also hit with the ransomware.
Ransomware attacks are on the rise around the world. Have you paid the ransom?
The Shadow Brokers released Eternal Blue as part of a trove of hacking tools that they said belonged to the US spy agency.
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