The programme uses a centralised database to update individual computers with a list of banned content.

Chinese officials have said it is designed to filter out pornography and protect children, but computer experts have warned that the software could be used to collect private data or personal information, and to monitor for potential online dissent.

'Great Firewall'

"From any point of view this is a piece of software that is very close to and is functionality-wise a piece of spyware"

Charles Mok,
chairman of the Hong Kong chapter of the Internet Society

Mok said that China already operates a sophisticated internet screening at the server level – dubbed the Great Firewall of China – but he said that implementing screening measures at the PC level was unique.

He said the directive had generated considerable discussion in online Chinese forums, with many noting that the software can be uninstalled by users.

"But I think the vast majority of users would not bother or not have the knowledge of how to do that," Mok said.

"If any other company tried to say that I want to install a piece of software onto your system, people would worry that it's a piece of spyware. But now it comes from the government, so what do you call that?"

He said that in essence the software, after it was installed on a computer, "could still be operating as a piece of spyware".

"The system would have a centralised database and collect information about which websites people have been using and going to and so on," Mok said.

Dissidents

"From any point of view this is a piece of software that is very close to and is functionality-wise a piece of spyware."

China has a sophisticated system for monitoring the internet and blocking access to sites, chatrooms or services that authorities deem to be undesirable.

Companies such as Yahoo have been ordered by the government to hand over information that has then been used to prosecute political dissidents over material they have posted online or used in private emails.

Mok said he doubted however that the Green Dam software would enable authorities to have total control over the online environment.

"Whether or not this initiative will be sustainable is very doubtful because of the many technical operational complexities that will be involved if you're looking at the hundreds of millions of computers operating in China," he said.

"But the whole thing is about the message that is being sent – that 'you’d better watch out, I'm still continuing to watch you in one way or another'. And I think that psychological message is important."