Transcript for Law enforcement officials fear second wave of cyberattacks
George, now to that massive global cyberattack and fears it could spread this morning as millions return to work. Now, here's what we know. More than 200,000 computers have been hit across 150 countries targeting hospitals, schools, offices and train stations. The largest U.S. Target was FedEx. The attackers are demanding a ransom of 300 to $600. Our chief investigative correspondent Brian Ross is here with more details. Good morning, Brian. Reporter: Good morning. The FBI and law enforcement around the world on high alert this morning concerned the attackers will launch a second wave and the computers already infected over the weekend will only be detected this morning when they're turned on. Officials tracking the attack say it is the biggest of its kind in the history of the internet. The latest numbers are over 200,000 victims in 150 countries. Reporter: With great concern the worst may be yet to come this morning. Is this just the beginning? That's the concern that Monday when everyone returns to the office that this ransomware attack will be even larger. Reporter: The attack spread at a speed never seen before across six continents with an ominous message suddenly showing up on the targeted computers. Oops, your files have been encrypted and demand of 300 and $600 in ransom to free what are essentially the kidnapped locked up computers. Although officials say few have paid the ransom so far. There's been a remarkly low level of ransoms that have been paid. I think 20,000, 30,000 worth of dollars only. Reporter: It all could have been much worse but for the efforts of this computer security program in Indiana. He discovered there might be a kill switch. Once the kill switch was activated the malware would simply do nothing. It would not carry out its infection. Reporter: Huss' information was used by a 22-year-old programmer in great Britain who talked by phone with ABC news fearful to show his face. I was panicking looking through the code and I realized that actually, no, we had stopped it. Reporter: The biggest target in the U.S. Was FedEx shipping service. Elsewhere around the world factories, hospitals, even police departments were all hit. And this morning, they're trying to decide whether or not to pay up. Ironically the hackers used the same tools originally developed by the U.S. Intelligence to hack into foreign adversaries that got leaked last month and now the tools are using it against us. Best stress for anyone using Microsoft to install all the upgrades the company offers which does provide a patch or a fix for this. George. Okay, Brian, thanks.
This transcript has been automatically generated and may not be 100% accurate.