The company has a wide range of activities from naval electronics, network and protection systems, electronic warfare and global communications, according to its website.

Along with European partners, Leonardo is involved in the MBDA group that makes several kinds of missiles, for example.

"At the end of a complex investigation by the Naples prosecutor into a serious computer attack against Leonardo .. a former worker and a company director were arrested," a ministry statement said.

A programme inserted into dozens of work computers via a USB stick at the company's plant in Pomigliano d'Arco, near Naples, allowed hackers to harvest data on projects, including strategic ones, over a two-year period.

The attack was uncovered by a computer crime unit at the prosecutor's office, which issued arrest warrants for illegal access to a computer system, interception of IT communications and illegal use of personal data.

The head of Leonardo's anti-hacking unit was also arrested for obstructing the investigation and providing false information on the nature of the attacks and their effects.

Investigators said that from May 2015 until January 2017, the group's IT system was targeted by an "Advanced persistent threat" led by a worker tasked with keeping the computers secure.

They did not provide extensive details on which systems had been hacked

In January 2017, Leonardo officials uncovered abnormal data traffic from work stations that was generated by so-called malware dubbed "cftmon.exe".

Hackers were able to intercept messages that were typed into the computers and capture images from their screens.

Some of the work stations were used to create strategic products and services for Italy's defence.

A total of 94 computers were compromised, including 48 that belonged to companies working in the aerospace sector.

No less than 10 gigabytes of data, equivalent to around 100,000 files, were lifted from the plant in Pomigliano d'Arco, including information on components of civilian and military aircraft.

Leaonardo said in a statement: "The company, which is obviously the injured party in this affair, has provided maximum cooperation since the beginning and will continue to do so to enable the investigators to clarify the incident, and for its own protection.

"It should be noted that classified or strategic data is processed in segregated areas, without connectivity, and not within the Pomigliano plant.