A Chinese software programmer has sparked a spying row after he was arrested last week trying to steal software used in the seismic imaging of oil fields.

Shan Yan Ming, 32, has been in the US since the end of April as part of a contract between the state-owned China National Petroleum Corporation and US company 3DGeo Development.

He had been training in the use of the company's software, but was caught trying to use a password to download expensive company software to a portable computer.

FBI and local law enforcement officials later arrested him at the San Francisco International Airport as he attempted to flee the country and return to China.

Dimitri Bevc, president and co-founder of 3DGeo, told the New York Times: "He was trying to gain access to our high-end seismic imaging software, which is proprietary."

Silicon Valley companies have frequently been the target of both industrial and government espionage and it is uncertain if Ming was spying for government, private enterprise or for personal use.

It is the second time executives at the software development company have found a Chinese employee trying to steal software. The earlier case, some five years ago, was not reported.

The company had been watching Ming because they were aware that he was a security risk.

According to 3DGeo officials, the programmer had a software tool that can be used to extract stored and encrypted passwords.

But they said they did not believe the program had been used successfully. Instead, Ming might have observed another employee entering the password and then copied it.