There have been four major attacks on Airbus in the last 12 months, according to two security sources involved in investigating the hacking.

The group has long been considered a tempting target because of the cutting-edge technologies that have made it one of the world's biggest commercial plane manufacturers, as well as a strategic military supplier.

In January, it admitted to a security incident that had "resulted in unauthorised access to data", but people with knowledge of the attacks outlined a concerted and far bigger operation over the last year.

Hackers have targeted British engine-maker Rolls-Royce and the French technology consultancy and supplier Expleo, as well as two other French contractors working for Airbus that AFP was unable to identify.

Romain Bottan of the aerospace security specialist BoostAerospace said the attacks showed that hackers were seeking out weak links in the chain to compromise Airbus's systems.

"Very large companies are very well protected, it's hard to pirate them, so smaller companies are a better target," he said.

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