the united states, but american computers along with the rest of the world could still be at risk. the big key here is whether or not your computers or computer networks have been updated with the latest security patches from microsoft. chris? >> meantime, a researcher who is believed to have stopped the attack over the weekend is talking about how he did it. what do we know? >> reporter: yeah, it's a little bit technical when you get into the weeds about how exactly he activated this kill-switch. but he's a 22-year-old cyber security researcher. he says he first noticed the attack friday morning, didn't think much of it at first, until he saw it spreading across hospitals in england and scotland. he says he found a domain name that was linked to this malware. he registered it and noticed the virus slowed down in how quickly it was spreading. he also said, chris, that he was surprised by its lack of sophistication. he said it looked like something that someone had written in their free time, which may offer