Foreign hackers were behind a cyberattack on the website of Lazio, the Italian region that includes Rome, where all bookings for the coronavirus vaccines were suspended, officials said Monday.
"The attacks are ongoing, the situation is very serious indeed," regional chief Nicola Zingaretti told a press conference as the head of Italy's spy agency was called to address parliament's security committee on the incident.
The hack, "by persons unknown... from outside the country", was launched on Saturday night and brought vaccine bookings to a juddering halt.
"The attack was very powerful... Probably the most serious ever launched on our national territory," Zingaretti said, describing the hackers as "criminal or terrorist".
All computer servers in the regional government in Lazio have been shut down in a bid to stop the virus spreading.
The attackers used ransomware, a form of malware that encrypts the victim's files, a regional official said.
A ransom, usually in bitcoins, is demanded in exchange for the key to decrypt the data.
However, no ransom request had yet been made for the Lazio website, Zingaretti said.
The main fallout was the halt on future bookings for Covid-19 vaccinations. Jabs already reserved until August 13 would go ahead, he said.
Some 66 percent of the adult population in Lazio have been vaccinated, according to officials.
Nationwide, 60 percent of Italy's population over 12 years old has been fully vaccinated, with 68.5 million total doses administered.
In June the Italian government set up a new agency specialised in cybersecurity in order to fight against an increasing number of attacks.