More than $500 million worth of pirated software, including counterfeit Microsoft and Symantec products, has been seized in a long-running joint probe by Chinese police and the FBI, officials from both countries said on Tuesday.

The operation began in 2005 and has led to 25 arrests and the smashing of several pirating syndicates in China that were making and distributing counterfeit software around the world, mostly to the United States.

Widespread intellectual property rights violations across a range of industries, including software, music, movies and fashion, have been a major source of friction between China and major trade partners the United States and Europe.

Details of what officials called the "unprecedented co-operative effort" between China's policing ministry and the FBI were unveiled to the media at an intellectual property conference in the southern Chinese city of Shenzhen.

More than 290,000 counterfeit software CDs and certificates of authenticity have been seized in the operation.

Six manufacturing and retail facilities were dismantled and 47,000 counterfeit Microsoft CDs seized, as well as equipment to manufacture Symantec computer software products.

The FBI estimated the retail value of the software seized at more than $500 million.

According to the US Chamber of Commerce, counterfeiting and piracy costs the United States economy about 250 billion dollars annually.