WannaCry spread incredibly rapidly due to its ability to spread through office networks once one PC was infected.
Broadcaster NTV said 600 companies and 2,000 computers in Japan had been affected.
The scope of the attacks was not immediately clear, but some analysts reported that dozens of countries had been affected, with the malware linked to attacks on hospitals in Britain as well as the Spanish telecom giant Telefonica and the USA delivery firm FedEx. Bossert said the USA hasn't ruled out involvement by a foreign government, but that the recent ransom demands suggest a criminal network. One did not include the so-called kill switch that allowed researchers to interrupt the malware's spread Friday by diverting it to a dead end on the internet.
Meanwhile, at Indonesia's biggest cancer hospital, Dharmais Hospital in Jakarta, around 100-200 people packed waiting rooms after the institution was hit by cyber attacks affecting scores of computers on Sunday, Reuters reported. It appears to have hit first in Britain, where it effectively shut down parts of the National Health Service. Two security firms - Kaspersky Lab and Avast - said they had identified the malicious software behind the attack in over 70 countries, although both said the attack had hit Russian Federation the hardest.
Computers booting up to start the workweek might continue the spread of "WannaCry", a ransomware attack where hackers lock down a computer and threaten to delete all its data unless a ransom is paid.
According to the company, "customers who are running supported versions of the operating system (Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8.1, Windows Server 2012, Windows 10, Windows Server 2012 R2, Windows Server 2016) will have received the security update MS17-010 in March".
Shares in firms that provide cyber security services rose with the prospect that companies and governments would have to spend more money on defences.
Once WeCry began spreading, however, Microsoft took the "highly unusual" step of releasing free security updates for those out-of-support versions of Windows, which can be downloaded from its website.
Chinese state media reported Monday that more than 29,000 institutions across the country - including universities, railway stations, hospitals and gas stations - had been infected. Authorities recommended that victims not pay, but even a small fraction of successful ransoms would net the attackers a considerable amount of money. "It's like after a robber enters your home". "We haven't fully dodged this bullet at all until we're patched against the vulnerability itself". Less common are actual changes that happen fast enough to make a difference.
It comes after more than 200,000 victims in around 150 countries were infected by the ransomware which originated in the United Kingdom and Spain on Friday before spreading around the world. Bloomberg saysthat the hackers have made as much as $50,000 from the ransomware.
"I am anxious about how the numbers will continue to grow when people go to work and turn [on] their machines", Rob Wainwright, director of the European investigative agency Europol, told NBC News' U.K. partner ITV on Sunday.
Microsoft's president and top lawyer said Sunday that the ongoing cyberattacks, which experts are calling the largest in history, should be a "wake-up call" for governments - especially the U.S.
The NSA is widely believed to have developed the hacking tool that was leaked online in April and used as a catalyst for the ransomware attack.
Researchers who helped prevent the spread of the malware and cybersecurity firms worked around the clock over the weekend to monitor the situation and install the software patch.
"Right now, just about every IT department has been working all weekend rolling this out", Dan Wire, spokesman at Fireeye Security, said.
Microsoft's top lawyer has called on governments around the world to treat the global cyber attack as a "wake-up call" as he laid part of the blame at the door of the U.S. administration.