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.
