49-year-old Chunlai Yang, who is a naturalised US citizen and had worked at the exchange for 11 years, was arrested at his desk at the CME's Chicago HQ.

The arrest followed an internal investigation by the CME which discovered that Yang had downloaded and copied thousands of files to his computer and removable storage devices.

"Many of the downloaded files were critical to the operation of the CME group and are considered proprietary in nature and contain protected source code," says the FBI.

Subsequent investigation by the FBI determined that Yang had also been in e-mail contact with the assistant director of the Logistics and Trade Bureau for the Zhangiagang Free Trade Zone. One of the e-mails sent by Yang contained an attachment, which was a CME document containing protected source code and proprietary information.

Yang, who had booked a one-way flight to China, scheduled to depart from O'Hare Airport on 7 July, had also been in contact with two individuals who were the sole shareholders and officers of East China Technology Innovation Park Company, a Hong Kong firm in which Yang had invested $118,182.

The e-mails show that the company wanted to set up a futures exchange in China and sell trading software.

If found guilty, Yang faces a possible sentence of up to 10 years' incarceration, a $250,000 fine, and three years of supervised release.