By Mark Ward
Technology Correspondent, BBC News website
Around 20% of the world's hijacked computers sending out spam, attacking websites and hosting unsavoury material are in China, says a report.
Net use is taking off in China
The figures, from security firm Ciphertrust, come amid spiralling rates of internet use in China.
China already has the second biggest net-using population in the world, even though only 8% of its people go online.
Now spam and viruses are becoming big problems, since the government relaxed controls on the net, an expert says.
Net use is growing fast and by 2007 the number of people using broadband in China should surpass those in the US.
But China is not just keeping up on ordinary net use and users, it is also setting the pace on computer crime too.
Typically the hijacked PCs fall under the remote control by malicious hackers when the machines fell victim to a virus such as a worm or Trojan.
Often the controllers of these so-called zombies do not live in the same nation as the machines under their sway.
Ironically much of the spam sent via these hijacked machines may not reach Chinese people at all.
But, said Jamz Yaneza, a senior anti-virus consultant at Trend Micro and an expert on the Chinese net experience, this does not mean that Chinese people are free of the problems so familiar to Western net users.
He said problems of spam, viruses and the like have recently started to cause big problems in China.
Computers and the net are reaching everyone in China
Trend Micro has signed a deal with Chinese net service firm Sina.com to help it deal with virus outbreaks and other computer crimes and misdemeanours.
Mr Yaneza said virus outbreaks, spam and phishing have only recently become a significant problem for Chinese net users.
"It's only taken off taken off ever since government removed some of the controls which helped avoid what's happened to the rest of the world," he said.
The Chinese government controls where people can access the net, which sites they can look at, the news they get and the topics for discussion in chat rooms.
This rigid control helped to limit the effect of viruses and spam but problems have started to emerge now that some controls are being relaxed, said Mr Yaneza.
This has let in many of the spam, phishing and virus laden e-mail messages that would otherwise be stopped.
The only types of e-mail scam that Chinese net users do not fall victim to is phishing scams that ask for credit card details. Hardly anyone in China has a credit card, said Mr Yaneza.
But Chinese people are staggeringly likely to get hit by other attacks. Recent statistics suggest that 80% of Chinese net users have fallen victim to a computer virus.
Computers are too costly for many Chinese people
Part of this might be because many Chinese net users open up English language e-mail messages just to see what they say.
Mr Yaneza said English is seen as the language of business and something that Chinese people are keen to be familiar with, hence their willingness to click on unsolicited messages.
Chinese people are also less likely to pick out the scrambled spelling, such as V1agra, that to many Westerners signifies spam.
"The odd formatting is not going to be strange to them," he said, "they expect that because e-mail has gone through so many filters."
Chinese spam has a character all its own, said Mr Yaneza. By contrast to Japanese spam which is predominantly sexual, Chinese junk mail plays on people's aspirations.
Mr Yaneza said Chinese spam was about free loans for schooling or further education, learning a language or to help someone expand their business.
"Looking at spam teaches you something about the culture," said Mr Yaneza.