Cybersecurity firm Symantec Corp. said on Monday it was "highly likely" a hacking group affiliated with North Korea was behind the "WannaCry" cyberattack this month that infected more than 300,000 computers worldwide and disrupted hospitals, banks and schools across the globe.

Symantec researchers said they had found multiple instances of code that had been used both in the North Korea-linked group's previous activity and in early versions of WannaCry.

In addition, the same Internet connection was used to install an early version of WannaCry on two computers and to communicate with a tool that destroyed files at Sony Pictures Entertainment. The U.S. government and private companies have accused North Korea in the 2014 Sony attack.