LONDON -- Employees booting up computers at work Monday could see red as they discover they're victims of a global "ransomware" cyberattack that created chaos in 150 countries and could wreak even greater havoc as more malicious variations appear.
As a loose global network of cybersecurity experts fought the ransomware hackers, officials and experts on Sunday urged organizations and companies to update older Microsoft operating systems immediately to ensure they aren't vulnerable to a more powerful version of the software - or to future versions that can't be stopped.
The initial attack, known as "WannaCry," paralyzed computers that run Britain's hospital network, Germany's national railway and scores of other companies and government agencies worldwide in what was believed to be the biggest online extortion scheme so far.
Chinese media reported that more than 29,000 institutions in the country had been struck by Saturday evening, with universities and other educational entities the hardest hit, along with railway services and retailers. Japanese broadcaster NTV reported 600 companies in that country had been hit, and automaker Nissan and the Hitachi conglomerate said they were addressing the problem at their affected units. Officials in Japan and South Korea said they believed security updates had helped ward off the worst of the impact.
The full extent of the attack won't become fully clear until more people return to their workplaces Monday for the first time since the attack. Many may click infected email attachments or bad links and spread the virus further.
"It's this constant battle," said Ryan O'Leary, vice president of WhiteHat Security's threat research center. "The bad guys are always one step ahead."
Microsoft blamed the U.S. government for "stockpiling" the software code that was used by unknown hackers to launch the attacks. The hackers exploited software code from the National Security Agency that had leaked online.
The company's top lawyer said the government should report weaknesses it discovers to software companies rather than seek to exploit them.
"An equivalent scenario with conventional weapons would be the U.S. military having some of its Tomahawk missiles stolen," attorney Brad Smith wrote on Microsoft's blog.
New variants of the rapidly replicating worm were discovered Sunday and one didn't include the so-called kill switch that enabled researchers to interrupt its spread Friday by diverting it to a dead end on the internet.
Ryan Kalember, senior vice president at Proofpoint Inc. which helped stop its spread, said the version without a kill switch was able to spread but was benign because it contained a flaw that wouldn't enable it to take over a computer and demand ransom to unlock files. However, he said it's only a matter of time before a malevolent version surfaces.
"I still expect another to pop up and be fully operational," Kalember said. "We haven't fully dodged this bullet at all until we're patched against the vulnerability itself."
The attack held users hostage by freezing their computers, popping up a red screen with the words, "Oops, your files have been encrypted!" and demanding money through online bitcoin payment - $300 at first, rising to $600 before it destroys files hours later.
The ransomware attack was particularly malicious because if just one person in an organization clicked on an infected attachment or bad link, all the computers in a network would be infected, said Vikram Thakur, technical director of Symantec Security Response.
"That's what makes this more troubling than ransomware was a week ago," Thakur said.
It hit 200,000 victims across the world since Friday and is seen as an "escalating threat," said Rob Wainwright, the head of Europol, Europe's policing agency.
"The numbers are still going up," Wainwright said. "We've seen that the slowdown of the infection rate over Friday night, after a temporary fix around it, has now been overcome by a second variation the criminals have released."
The effects were felt around the globe, disrupting computers that run factories, banks, government agencies and transport systems in nations as diverse as Russia, Ukraine, Brazil, Spain, India, Indonesia and the U.S. Britain's National Health Service was hit hard, while Russia's Interior Ministry and companies including Spain's Telefonica, FedEx Corp. in the U.S. and French automaker Renault all reported disruptions.
White House officials told CBS News President Trump ordered "emergency meetings" Friday night and Saturday to address the global cyberattack. Details of what was discussed weren't revealed.
It was too early to say who was behind the onslaught, which struck 100,000 organizations, and what their motivation was, aside from the obvious demand for money. So far, not many people have paid the ransom demanded by the malware, Europol spokesman Jan Op Gen Oorth told The Associated Press.
Researchers who helped prevent the spread of the malware and cybersecurity firms worked around the clock during the weekend to monitor the situation and install a software patch to block the worm from infecting computers in corporations across the U.S., Europe and Asia.
"Right now, just about every IT department has been working all weekend rolling this out," said Dan Wire, spokesman at Fireeye Security.
Businesses, government agencies and other organizations were urged to quickly implement a patch released by Microsoft Corp. The ransomware exploits older versions of Microsoft's operating system software, such as Windows XP.
Installing the patch is one way to secure computers against the virus. The other is to disable a type of software that connects computers to printers and faxes, which the virus exploits, O'Leary added.
Microsoft distributed a patch two months ago that could have forestalled much of the attack, but in many organizations it was likely lost among the blizzard of updates and patches that large corporations and governments strain to manage.
"It's one of those things, in a perfect world, if people were up to date on the patches, this wouldn't be a problem," O'Leary said. "But there are so many things to patch. The patch lists can be ginormous. It can be tough to tell which patch is important, until it is too late."