Meanwhile, new versions of the ransomware have reportedly surfaced, including one without the kill switch exploited by a 22-year-old computer security researcher to shut the attack down.
The virus has hit at least 150 countries and claimed 200,000 victims, according to the European Union's law enforcement agency Europol. But computers and networks that didn't update their systems were still at risk.
He has compared Friday's cyber attack to a scenario of the United States military having some of its Tomahawk missiles stolen.
(AP Photo/Mark Schiefelbein). A screenshot of the warning screen from a purported ransomware attack, as captured by a computer user in Taiwan, is seen on laptop in Beijing, Saturday, May 13, 2017.
In the event that a computer is infected with malware, experts say that users should not pay the ransom as there is no guarantee that the files will be returned and whether the perpetrators will refrain from attacking the user again.
U.S. Treasury Secretary Steven Mnuchin, at a meeting of world leaders in Italy, said the attack was a reminder of the importance of cybersecurity.
The attacks exploit a vulnerability in outdated versions of Microsoft Windows that is particularly problematic for corporations that don't automatically update their systems.
Officials and experts Sunday urged organizations and companies to update their operating systems immediately to ensure they aren't vulnerable to a second, more powerful version of the software - or to future versions that can't be stopped. And while Microsoft had already released a security update to patch the vulnerability one month earlier, the sequence of events fed speculation that the NSA hadn't told the US tech giant about the security risk until after it had been stolen.More news: Atria Investments LLC Has $457000 Position in Morgan Stanley (MS)
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The virus took control of users' files and demanded $300 payments to restore access, the BBC report said.
Some organizations around the world will likely wake up to computers infected by the ransomware, causing it to potentially spread even further.
A cybersecurity researcher has been credited with slowing the ransomware after accidentally discovering a "kill switch" that could prevent the spread.
"Just patch their systems as soon as possible", MalwareTech said. More than 200,000 computers have been affected so far.
Firstly, you're only likely to be affected if you use a Windows operating system.
Don't grumble when your system administrator at work takes the network down periodically to update systems, which usually includes installing new and often critical software patches. They, too, should regularly update with software patches as they're issued.
In China, the internet security company Qihoo360 issued a "red alert" saying that a large number of colleges and students in the country had been affected by the ransomware, which is also referred to as WannaCrypt.
The hackers are believed to have used "cyber weapons" stolen from the US' National Security Agency to lock up computers and hold users' files for ransom.