WHAT IS HAPPENING?

The ransomware, called "WannaCry," locks down all the files on an infected computer and asks the computer's administrator to pay in order to regain control of them. The exploit was leaked last month as part of a trove of NSA spy tools. 

The ransomware is spread by taking advantage of a Windows vulnerability that Microsoft (MSFT, Tech30) released a security patch for in March. But computers and networks that hadn't updated their systems were still at risk. 

In the wake of the attack, Microsoft said it had taken the "highly unusual step" of releasing a patch for computers running older operating systems including Windows XP, Windows 8 and Windows Server 2003. 

"Affected machines have six hours to pay up and every few hours the ransom goes up," said Kurt Baumgartner, the principal security researcher at security firm Kaspersky Lab. "Most folks that have paid up appear to have paid the initial $300 in the first few hours."

Sixteen National Health Service (NHS) organizations in the UK have been hit, and some of those hospitals have canceled outpatient appointments and told people to avoid emergency departments if possible.

When CNNTech first reported the Microsoft vulnerabilities leaked in April, Hickey said they were the "most damaging" he'd seen in several years, and warned that businesses would be most at risk. 

HOW TO PROTECT YOURSELF

Consumers who have up-to-date software are protected from this ransomware. Here's how to turn automatic updates on.

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*This blog post is excerpts from the original article on money.cnn.com