The hacking attack sought to exploit a software vulnerability, ACN director general Roberto Baldoni told Reuters, adding it was on a massive scale.

Italy's ANSA news agency, citing the ACN, reported that servers had been compromised in other European countries such as France and Finland as well as the United States and Canada.

Dozens of Italian organisations were likely to have been affected and many more had been warned to take action to avoid being locked out of their systems.

Telecom Italia customers reported internet problems earlier on Sunday, but the two issues were not believed to be related.

U.S. cybersecurity officials said they were assessing the impact of the reported incidents.

"CISA is working with our public and private sector partners to assess the impacts of these reported incidents and providing assistance where needed," the U.S. Cybersecurity and Infrastructure Security Agency said.