Among those affected in the US were hospitals, the pharmaceutical company Merck, Nabisco and Oreo. A major Los Angeles port was forced to stop operations yesterday because of the attack and was still closed as of this morning. FedEx also experienced disruptions in its TNT Express delivery service. A US nuclear power plant was the victim of a cyberattack as well, but it's not as of yet clear whether it was connected to the others.

The virus being spread is thought to be a version of the "Petya" ransomware and like the WannaCry virus that wreaked international havoc in May, it appears to take advantage of a Microsoft Windows flaw uncovered by the NSA and published online by hackers. This virus, however, seems to only be able to spread between directly connected networks, which is believed to be the reason the attack seemed to slow throughout the day Tuesday.

It's still unclear as of now who is behind the attack.