Hacking hero who saved UK from cyber attack
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Hacking hero who saved UK from cyber attack

16 May 2017 Last updated at 06:48 BST

A massive cyber attack on computer networks around the world caused chaos on Friday.

A harmful computer program called WannaCry started taking over people's computer files and demanding money to let them back into their own systems.

But how was it stopped? Well, 22-year-old Marcus - a UK security researcher who has his own company - helped to limit the damage.

He's being called an "accidental hero" after registering a domain name to track the spread of the virus, which actually ended up stopping it from spreading!