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A 22-year-old British computer expert who's credited with slowing the WannaCry cyber-attack says he doesn't consider himself a hero.

Marcus Hutchins says he fights attacks because "it's the right thing to do".

Since Friday, the cyber-attack has hit 150 countries and the NHS is still experiencing disruption.

In an interview with , Marcus said he and hundreds of experts at a Los Angeles-based computer firm worked to fight the virus.

Marcus, who's from Devon, found a so-called "kill-switch" which slowed the outbreak.

The WannaCry attack blocked people's files on their computer and demanded at least £230 ($300) to release them again.

Mostly users of older versions of Microsoft Windows were affected.

Marcus explained how he tackled the virus, saying he linked it to an unregistered web address.

Then he registered it, which seemed to stop it spreading.

His boss Salim Neino, CEO of Kryptos Logic, was full of praise.

"[Marcus] not only saved the United States but also prevented further damage to the rest of the world," he said.

"Within a few moments, we were able to validate that there was indeed a kill switch. It was a very exciting moment. This is something that Marcus validated himself."

Despite the damage it has caused, Marcus and his workmates claim the virus was "poorly designed", with an unsophisticated payment system.

Marcus could be on his way to a life of online fame now, as he's reportedly been in touch with the FBI, as well as cyber security officials.

Right now though, he's going on holiday to Las Vegas and California.

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