Italian police have arrested two people for hacking into the emails of European Central Bank President Mario Draghi, former Prime Minister Matteo Renzi and thousands of other accounts.

The Rome court ordered the arrest of Giulio Occhionero, 45, and his sister Francesca Maria Occhionero, 48, for stealing state secrets and illegal hacking.

"There were tens of thousands of email accounts hacked, and among them were accounts belonging to bankers, businessmen and even several cardinals in the Vatican," said Roberto Di Legami, director of the specialised cyber police unit that conducted the investigation.

Mr Occhionero, a nuclear engineer by training, developed the malware that infected the email accounts and allowed him access to all correspondence, Mr Di Legami said.

The emails were probably used by Ms Occhionero, who heads an investment firm called Westland Securities, "to make investments based on reserved information," Mr Di Legami said.

Mr Draghi's account at the Bank of Italy, where he was previously governor, and Mr Renzi's account while he was prime minister were among those infected by the malware, according to the arrest warrant.

Mr Draghi's ECB account was not listed as having been targeted in the warrant.

While most of the hacking appears to have been focused on the email accounts, there was evidence that Mr Occhionero had managed to install a key logger on some computers, allowing him to see every keystroke, Mr Di Legami said.

According to the material already seized in Rome, some18,000 accounts may have been hacked, and some 2,000 user passwords were found.

Former prime minister Mario Monti's accounts at Bocconi University, where he worked, and at the Senate also were targeted.

Vatican culture minister Cardinal Gianfranco Ravasi was another victim of the cyber attack.