They call it the Great Firewall of China - an elaborate system of software filters that dictates what internet content China's 100 million web users are allowed to access.

The Chinese Government uses it to weed out all the things it doesn't want its citizens reading about, listening to or watching.

As well as criticism of its policies and administration, the Government is adverse to "sex, violence and feudal superstitions", according to the official Chinese news agency, Xinhua. It's not keen on gambling either.

It means that if you are in China, there's no point Googling Tiananmen Square, Dalai Lama or anything triple-x in nature on Google.cn. You won't get the whole story.

Pen columns in the West about China's meddling in Tibet and it's unlikely anyone in China will ever get to read them.

We were shocked that an Asian broadcast of Prime Minister Helen Clark's interview on CNN was edited when she strayed onto the touchy subject of China's human rights record. The Chinese live with such interruptions every day.

As Clark pointed out: "Obviously China is not a democracy, and it is governed in a way that would not be acceptable in a Western democracy."

And neither is the internet governed in China as it would be in a Western democracy. According to a report released in April by the Open Net Initiative (http:/www.opennetinitiative.net/) China has the "most sophisticated internet-filtering regime" in the world and has increased censorship since the last report in 2002. China's internet monitoring taskforce numbers 30,000 people.

It's a different world, one where fear of defaming someone or embarrassing yourself are not the things holding you back from publishing your opinions on the internet, but the real risk of going to prison.

China's legacy of public infrastructure ownership means the Government has direct access to the fibre-optic networks that carry internet traffic in and out of the country.

They identify "objectionable" content by internet protocol (IP) address, searches for keywords and by domain name. I doubt that the Friends of Falun Gong website (www.fofg.org) gets any hits from China.

It's not just the big search engines and websites such as Sohu.com, Netease.com and Baidu.com that are monitored and filtered. Email messages, instant messenger conversations, weblog postings and bulletin board messages also pass through the filter. T he Chinese understand technology, so the filtering is very good - it's done in real time and is selective in nature. Sections of a website will often be blocked rather than the entire site.