Solid Oak Software Inc. has sued CBS Corp.'s (CBS) Internet unit for copyright infringement, alleging that its ZDNet China Web site helped firms backed by the Chinese government distribute a pirated software program aimed a censoring web content.

In a complaint filed Oct. 5 in a Los Angeles federal court, the Santa Barbara, Calif.-based software maker claims that CBS Interactive Inc. participated willingly in an effort by the Chinese government to give away tens of millions of versions of CyberSitter, a web content filtering program made by Solid Oak that blocks violent and pornographic web content.

Solid Oak wants at least $1.2 million in damages from CBS, which it says cooperated with Beijing by making a program called Green Dam available on its Web site for free download in order to promote the Web site and generate Web traffic and advertising revenue.

Green Dam was developed by two Chinese government-backed companies, Zhengzhou Jinhui Computer System Engineering Ltd. and Beijing Dazheng Human Language Technology Academy Ltd., according to the complaint. Independent researchers at the University of Michigan confirmed in June that Green Dam copied verbatim almost 3,000 lines of code from Solid Oak's 14-year-old program, which has more than 2.4 million active users, the complaint stated.

"We've reviewed the complaint and believe the allegations against CBS are without merit," CBS said in a statement. "As is evident from the complaint, this is a dispute between CyberSitter, the two Chinese companies that allegedly copied their filtering technology, as well as the Chinese government that backed these companies and the distribution of the allegedly infringing material."

Gregory Fayer, an attorney with Gipson Hoffman & Pancione who is representing Solid Oak, said the case has broad implications for software makers trying to protect themselves against large-scale international infringement of their intellectual property. He said Solid Oak is considering legal action against other parties involved in the case, but he rejected CBS' assertion that it's not liable.

"If you offer an illegal product for download on a web site, that's against the law," Fayer said.

The Chinese government earlier this year decreed that all PCs sold in China would be required to have Green Dam installed by July 1, claiming it was necessary to protect young people from unsavory Internet content, like pornographic and violent material. Human rights groups say the move is part of an effort to censor political and religious discourse on the web in China.

Solid Oak sent a cease and desist letter to CBS about the Green Dam download on Aug. 18, and CBS removed the download from its web site on Sept. 7, according to the complaint. It says CBS was aware that Green Dam was illegal since early June, at the latest, when the alleged infringement of its CyberSitter program was widely reported in the media.

-Nat Worden, Dow Jones Newswires; 212-416-2472; nat.worden@dowjones.com