The US Federal Bureau of Investigation is probing a series of cyber-espionage attacks on at least five major oil, gas and petrochemical companies by hackers based in China.

The attacks, which began more than a year ago and are continuing, have succeeded in capturing sensitive financial information, including plans for bidding on drilling rights in specific fields, and production information, such as the configuration of equipment.

Such data would be worthless to most people but highly valuable to competitors in the industry, suggesting an economic motive for the intruders. The penetration followed a similar pattern at all of the targets identified so far and appeared to have been conducted by a group of a dozen or fewer people working from about 9am to 5pm Beijing time during the week.