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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.

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To decode the files, the hackers were asking for $300 in ransom. The demand would double after three days, or data would be destroyed.

The so-called ransomware attack appears to exploit a weakness that was purportedly identified by the U.S. National Security Agency and leaked to the internet. It encrypts data on infected computers and demands payment before the information is unencrypted.

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.

Prime Minister Theresa May said it wasn’t just Britain.

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“This as not targeted at the NHS, it’s an international attack, and a number of countries and organizations have been affected,” she said.

That was an understatement. By the time she finished speaking, similar attacks had been reported on business targets across Europe including Spain’s telephone system. Japan, Turkey, and the Philippines were also affected.

In the U.S. FedEx was hit. Cyber security experts say the brunt of the attacks were felt in Russian, including the country’s largest mobile phone company. A statement from the delivery company Friday said its Windows-based systems were “experiencing interference” due to malware and that it was trying to fix the issue as quickly as possible.

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