China's controversial Green Dam web filtering software could affect US shipments of PCs to the country, after claims that the code uses stolen intellectual property from US firm Solid Oak Software.

Following an anonymous tip off on Thursday, Solid Oak said that the code contains substantial amounts of its own web filtering software known as CYBERSitter.

The company is therefore asking US manufacturers to halt shipments to China of PCs loaded with the Green Dam code.

"It is 100 per cent without a doubt our code that is included," said Jenna DiPasquale, Solid Oak's public relations manager. "At this point what we're focusing on is stopping US companies from shipping PCs to China with the software installed."
Green Dam was designed by Jinhui Computer System Engineering in China. Zhang Chenmin, the general manager of Jinhui, has reportedly denied that any of the code has been copied.

"I cannot deny that the two filters' databases of blacklisted URL addresses might share similarities. After all, they are all well-known international pornographic web sites that all porn filters are meant to block," Zhang told The China Daily. "But we didn't steal their programming code."

The Chinese government wants all computers sold in the country to include the Green Dam-Youth Escort software utility, which blocks pornographic web sites. All computers sold after 1 July should either have the software installed or included in CD format.

Although China has said that the software will not monitor and report back on users' viewing habits, the software has worried some privacy groups.

"We have already seen what many suspect is the Chinese government's use of software in this way," said Danny O'Brien, international outreach coordinator at the Electronic Frontier Foundation.

"A localised Chinese version of Skype included backdoors that passed on private IM conversations to third parties. Tibetan dissidents have struggled with key-logging spyware that is uniquely targeted to this political group."