A California software company plans to seek an injunction preventing U.S. companies from shipping computers with Chinese anti-pornography software that it claims was stolen, The Wall Street Journal reported on Saturday.

Solid Oak Software Inc said it found pieces of its CyberSitter Internet-filtering software in the Chinese program, including a list of terms to be blocked and instructions for updating the software.

Solid Oak representatives could not immediately be reached for comment on Saturday.

The Chinese company that made the filtering software, Jinhui Computer System Engineering Inc, denied stealing anything, the Journal said.

That's impossible, Jinhui's founder, Bryan Zhang, told the newspaper.

The Chinese government has required that all new computers made or shipped by July 1 must have Green Dam software pre-installed, to protect children against pornography.

Green Dam filters words and images, as well as web addresses.

Critics have said China's move raises issues of cyber-security and Internet freedom. Analysts said the action has also raised concerns among U.S. PC makers, including Dell Inc and Hewlett-Packard Corp, who fear they could face criticism in the West if they comply with the order.

China's PC market is forecast to be the world's largest by 2011, with nearly 50 million units shipped annually by 2012.

Solid Oak's president, Brian Milburn, told the Journal his firm received an anonymous email on Friday claiming that Green Dam may contain parts of his company's code. Milburn and his engineers compared the two programs and found many similarities.

I am 99.99 percent certain that if not the entire program at least a good proportion of it is stolen CyberSitter code, said Milburn, whose 15-employee firm is based in Santa Barbara, California.

According to some lawyers, Solid Oak faces a tough legal fight because the software will be sold only in China, the Journal said. The question would have to be settled by a Chinese court under Chinese law, one lawyer said.

The incident could add to an outcry over the lack of transparency in the Chinese government's decision to choose the Green Dam program to implement its filtering requirement.

(Reporting by Matthew Lewis; editing by Patricia Zengerle)