Massive cyberattack involving more than 100 countries, believed to be the biggest attack ever recorded

Tens of thousands of computer systems have fallen victim to hackers demanding ransom.
2:05 | 05/13/17

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Transcript for Massive cyberattack involving more than 100 countries, believed to be the biggest attack ever recorded
day long on ABC newsnews.com. We move on to the global cyberattack. Tens of thousands of computer sidss in nearly 100 countries have been victimized. Hackers demanding ransom. This attack began with what's called a simple phishing e-mail and quickly spread affecting FedEx and crippling some hospitals over in the uk. ABC's Jennifer Eccleston is in London with more. Reporter: The massive and coordinated cyberattack wreaking global havoc infecting 9 countries. A malware virus known as wannacry attacking tens of thousands of computers in company, universities and hospitals. Hackers demanding money to unlock critical files. It's attacking a loophole seems to be in the Microsoft software and exploiting tools that were stolen from the national security agency. Reporter: Shipping giant FedEx not immune. Hit by the virus Friday. And in the uk, a national health emergency, dozens of hospital computers hijacked. We're aware that a number of nhs organizations have reported that they have suffered from the ransomware attack. Reporter: This screen grab from a national health service computer, a message from the assaila assailants, pay up in Bitcoin, the equivalent of $300 or the critical files disappear. The assault crippling hospitals. Many urging noncritical patients to stay home. I think it's a heinous crime, this hacking, because they're putting people's lives at risk. Reporter: The department of homeland security issuing a atement saying, that they stand ready to lend technical support and assistance as needed to our partners, both in the United States and internationally. Now, Microsoft released a patch to fix the loophole in March but where that upgrade was not installed, those networks remain vulnerable. The company saying in a statement, they are working with customers to provide additional assistance as this situation evolves. Dan and Paula. So much concern about global vulnerability to cyberattacks on so many levels. This is not going away. Jennifer, thank you very much.

This transcript has been automatically generated and may not be 100% accurate.

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