The global cyber attack that hit 150 countries is "highly likely" to have been perpetrated by hackers in North Korea, cyber security researchers have said.

Researchers at Symantec have found compelling evidence linking the ransomware attack to hackers associated with North Korea called the Lazarus Group.

The findings confirm reports in the immediate aftermath of the attack, which affected more than 300,000 machines at organisations including the NHS, Nissan and Telefonica, that attackers linked to North Korea were to blame.

The experts have connected the source of WannaCry with the computers behind the Sony Pictures Entertainment hack in 2014. The same internet connection used to destroy files associated with The Interview was used to install an early version of WannaCry, Symantec said.

Symantec has previously linked Lazarus to the banking hack that let hackers steal $81 million from Bangladesh's central bank last year.