Organisations across the world have been the victims of widespread disruption as the second major cyber attack in a matter of months has struck.
Several computer systems in a number of Irish offices of international companies, such as Danish shipping firm Maersk and pharmaceutical company MSD, are among those affected.
According to RTÉ, a cyber security consultant warned that Government agencies and banks in Ireland are ''at risk of attack''.
A US hospital also fell victim, and Cadbury owner Mondelez International said it also had experienced a "global IT outage".
Blame is being directed at intelligence agencies in the US such as the CIA and the National Security Agency, as they were accused of "stockpiling" software code, allowing easier access to exploitation by hackers.