By Maggie Shiels
Technology reporter, BBC News, Silicon Valley
Computer makers that don't install Green Dam face possible penalties
A California company is considering legal action to prevent computers being shipped to China with what it says is stolen internet blocking software.
Solid Oak said it found pieces of its CyberSitter programme in China's Green Dam Youth Escort screening software.
China has mandated that all new PCs contain filters to protect children from offensive material on the net.
The Chinese firm that made Green Dam, Jinhui Computer System Engineering Inc, denies any wrongdoing.
But Solid Oak's Brian Milburn said "We're contacting Dell, HP and others to stop compromised material being shipped."
"If China had gotten hold of free pirated copies of Microsoft's Windows and told Dell and HP to put this on all computers you ship, you would hear a loud outcry. China has a very loose interpretation of what is intellectual property," said Mr Milburn.
He told the BBC that as far as he was aware, the compromised software containing code from CyberSitter has already been installed on 9 million computers in China.
The Chinese government has required that all new computers made or shipped by 1 July have Green Dam pre-installed.
The government's controls over what its citizens can see online is often referred to as the "Great Firewall of China."
Mr Millburn, whose company is based in Santa Barbara, said US computer manufacturers were being put in the middle of a row not of their making.
The system reportedly blocks legitimate as well as banned content
"It's not their fault and I don't want to sound like that. They are stuck in the middle. I want to do the right thing and maybe it will give them an opportunity to get out of distributing machines with this software."
Critics say the software will be used to prevent China's 250 million internet users from searching for politically sensitive information. Green Dam filters words and images as well as web addresses.
"While the justification may be pitched as protecting children and mostly concerning pornography, once the architecture is set up it can be used for broader purposes, such as the filtering of political ideas," Professor Jonathan Zittrain of Harvard's Berkman Centre told the BBC last week.
A report by the OpenNet Initiative has found that Green Dam can monitor activities outside of web browsing and can terminate applications.
Dell, the world's second biggest PC seller, said no machines had been shipped containing Green Dam.
"We are aware of the policy from China and along with the rest of the industry are reviewing it," said spokesman David Frink.
It has been estimated that in the next two years China's PC market will be the world's largest with 50 million units shipped annually by 2012.
Solid Oak's founder Mr Milburn said he was first alerted there was a problem on Friday when he received an email from someone claiming to be from the Chinese Communist Party.
Cybersitter is aimed at helping parents control what their children see online
"At first I thought it was a prank and didn't pay much attention to it," Mr Milburn told the BBC.
"One of our employees researched it and came back to me and said I might want to look at it more closely. We then found actual proprietary code from CyberSitter within the Green Dam programme that is only available in an encrypted format.
"I spent a good deal of the weekend with another engineer trying to find if it was an honest mistake. But someone made a 100% conscious effort to do this. This is not some accident," stated Mr Milburn.
A report by the University of Michigan has also accused the Chinese vendor of using material from Solid Oak Software's product.
Added to that the study found serious vulnerabilities that could allow hackers to hijack PCs running the Chinese software.
China's Ministry of Industry and Information Technology has ordered the problem be fixed.
The Chinese company that made the filtering software told China Daily that it has been wrongly accused.
Every new computer in China will have the software installed
"That's impossible. We didn't steal their programming code, " said Bryan Zhang of Jinhui Computer System Engineering Inc.
Mr Milburn said even though legal action against the Chinese developer is one thing he is looking at, he is not sure it will be worth the effort.
"We are just a little company and trying to take on China is an impossible task. We don't want to turn into a litigation company."
Mr Milburn said Solid Oak will also file a complaint with the FBI's Computer Crime Task Force.
Online surveys conducted by some of China's most popular web portals like sina.com and shou.com showed that four out of five netizens will not use the Green Dam software or have it installed.