Pirated software worth $500m (£250m) has been seized as the FBI shuts down a world-spanning piracy outfit.
The pirates pumped out fake versions of Windows Vista
Before the raids the Chinese counterfeiting syndicate was thought to have sold and distributed software worth more than $2bn.
The FBI and China's Public Security Bureau arrested 25 people during the two-week operation against the pirates.
Despite recent crackdowns, industry figures suggest that 82% of the software used in China is counterfeit.
The FBI said it had been building up a case against the piracy syndicate for years before staging the raids on the software production plants in China's Guangdong province.
During the raids, dubbed Operation Summer Solstice, the FBI seized more than 290,000 CDs with a claimed market value of $500m.
The gang was known to be producing pirated versions of 13 of Microsoft's most popular programs including Windows Vista, XP and Server as well as Office 2003 and 2007.
The syndicate sold versions of these programs in eight languages including Croatian and Dutch.
In a statement Microsoft said vital information that helped to track down the pirates came from its Windows Genuine Advantage (WGA) scheme.
WGA forces users of some versions of Windows to validate their copy of the operating system with Microsoft when updating their software.
Microsoft said information gathered by WGA from more than 1,000 fake copies produced by the counterfeiters and sold around the world helped law enforcement agencies home in on the pirates. Fake software produced by the group was found in 27 countries.
"Countries around the world are expected to experience a significant decrease in the volume of counterfeit software as a direct result of this action," said Microsoft in its statement.