It's safe to say that the internet is a battleground in China. It's where citizens turn first to seek information that's been censored by Communist state-run media -- but it's also where Communist authorities are pouring huge amounts of time and money in an attempt to block all information that casts the Party in a negative light.

Now internal documents leaked from the monitoring and censorship department of China’s leading search engine, Baidu, reveal how certain topics, words and websites are blocked from public viewing.

The documents show instructions, evaluation standards and a rewards system for censorship staff. They record internal activity in the department between November 2008 and March 2009.

Since the documents were leaked on the Internet, users have been widely posting them on blogs and forums, about as quickly as Chinese Internet censors are deleting them.

There are a total of 13 blacklisted topics, including the following: information on “defending human rights and appeals,” Falun Gong, the 1989 Tiananmen Square student massacre, information on Chinese Communist Party leaders, ethnic minority issues and the human organ trade. Under each topic is a list of keywords that they look for, such as “quit the CCP,” “dictatorship,” “suppression,” “China’s human rights” and “brainwashing.”

Last year, Citizen Lab from the University of Toronto published a report entitled “Search Monitor Project: Toward a Measure of Transparency.” It compared the transparency of search engines in China, including Google, Yahoo and Baidu. Baidu censored the most, more than 26% of the tested websites. But, also under pressure from Communist authorities, Western firms in China were hardly paragons of freedom: Yahoo censored 21% and Google 15%.