"In recent years, there have been many reports about cyber attacks in the media. In these reports, without any evidence, the parties concerned always pin the label of cyber attack on China and smear China," foreign ministry spokesman Geng Shuang said at a regular press briefing.

"This practice is neither professional nor responsible, and even has ulterior motives," Geng said, adding that China "is a firm defender of network security."

The hackers targeted Airbus suppliers -- British engine-maker Rolls-Royce, French technology consultancy and supplier Expleo, and two other French contractors -- in search of commercial secrets, according to security and industry sources who spoke to AFP on condition of anonymity.

None of the sources who spoke to AFP could formally identify the perpetrators of the attacks, pointing to the extreme difficulty in obtaining evidence and identification.

Many state-backed and independent hackers are known to disguise their tracks, or they may leave clues intended to confuse investigators or lead them to blame someone else.

But the sources said they suspected Chinese hackers were responsible, given their record of trying to steal sensitive commercial information and the fact that Beijing has just launched a plane designed to compete with Airbus and US rival Boeing.

sbr-lth/rox/mtp

AIRBUS GROUP

BOEING

ROLLS-ROYCE HOLDINGS