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MICHIGAN  —  A computer engineer in Michigan figured out how to stop what experts call the biggest cyberattack ever.

Authorities say a hacker or group of hackers created ransomware called WannaCry using stolen NSA tools. The software locks down all computer files and demands $300 to release them.

It spread quickly and impacted more than 200,000 computers in 150 countries. The attack even shut down emergency rooms in the U.K.

Security expert Darien Huss reverse engineered the program and found a kill switch the creator left in place to disable it. Huss says it looks like the coder that wrote the ransomware was not very experienced.

“We not only investigate attacks against our customers, we also investigate anything that’s going on around the globe. It really did not take long to figure out there was a kill switch feature in it,” he said. “This is probably one of the largest and widespread cyberattacks in the last 10 years. The individual or individuals responsible for this aren’t very sophisticated. It feels really amateur hour to me. The amount of law enforcement that are going to be investigating this, I really would not be surprised if the individual or individuals are apprehended. Personally, I really feel like I didn’t play a huge role in everything. All I really did is figure out that there was a kill switch feature. It just goes to show how interconnected our world is and how something so simple can have a devastating impact on everybody.”

A fellow security researcher in the U.K. helped Huss disable the ransomware.

Experts say so far, victims have paid about $32,000 to free their files. That number could rise when people go back to work on Monday.