The disruption of the Google search engine this month appears to have been only one symptom of a significant change in the way China censors the Internet. Observers say the main focus of the so-called Great Firewall has switched from preventing access to a long list of banned Web sites to screening Internet traffic, including e-mail, by searching out keywords and blocking the data they are associated with. A far greater amount of online information is being denied to mainland residents than was previously the case. Analysts and freedom of speech advocates say the move hurts China's attempts to portray a more progressive image to the world and unnecessarily violates people's privacy. The changes, which began to be noticed around September 13, are also proving highly unpopular with many of the country's 46 million Internet users. News sites, including the South China Morning Post's scmp.com, are particularly affected. Mainland users can still reach the scmp.com homepage, but if they try to read stories on topics Beijing considers politically sensitive, such as Falun Gong, Tibet or Taiwan independence, they are blocked. Even sites that offer seemingly benign information are tampered with. After being off-line for two weeks this month, Google now works when users put in most words. But looking for information on a banned topic can cause searches to be blocked until the browser is restarted. Mainland users claim e-mail has bounced back recently if messages contained the wrong words. One Beijing businessman said he sent a message regarding 'hardcore business negotiations', but was rejected because 'hardcore' implied pornography, which authorities want to block. Ted Ladd, a spokesman for US-based Websense, said it appeared Beijing was using a modified firewall. Instead of scanning for viruses, the system looks for banned content. Mr Ladd said keyword filtering was tried by schools and corporate users in North America, but fell out of favour because it blocked the good with the bad. He said screening out the word 'sex' would block 'Essex'. Screening 'breast' would block information on breast cancer. 'If you want to err on the side of caution, I guess it would be fine, but it is a very crude way of doing things,' Mr Ladd said. Analysts have said filtering Internet traffic on a nationwide scale was impossible as computers could not keep up with the data flow. But Internet activist Greg Walton said the experience of mainland users showed that China had a system powerful enough to do the job. The system is not foolproof - users report inconsistent blocks on e-mails and Web pages - but Mr Walton said time and technology were on the side of the censors, and the system would get better. 'It will be progressively cheaper and easier to collect, transport, store and analyse data,' he said. Bill Dong, spokesman for Dynamic Internet Technology, a company providing technical services to Voice of America's Chinese-language Web site, said keyword filtering had not replaced the block on previously banned sites, but had been added as an extra layer to selectively screen content on other sites. 'This is a way to get more extensive blocking without offending too many people,' he said. 'There is a Chinese saying, 'govern by separating'. So now, they do not have to block all of Google and offend everybody. They can block the Falun Gong part of a university site, for example, without offending students who need to get information there. So this will make their blocking socially easier.' Western firms such as Websense and Cisco have come under fire from freedom of speech advocates for providing China with technology to censor the Internet. But Nathan Midler, Asia-Pacific senior analyst with IDC in Beijing, said the new system appeared to be homegrown. Most of what is known about China's Internet censorship is speculation. Few outside Beijing's secretive security apparatus know what is going on and mainland authorities rarely comment on issues of national security. When Google and Alta Vista were re-routed or blocked, state officials denied involvement or refused to comment. Another key question is how long the new censoring will last. Some pundits believe the crackdown is driven by a desire for 'social harmony' leading up to the November 16th Communist Party Congress, and once the event passes, the tight grip on the Internet will be loosened. Others believe there has been a fundamental shift in the way Beijing views the Internet, with hawks who support censorship having more influence than doves who see more open access as a key to modernising society.