China wants all personal computers sold domestically to come with software that blocks access to online pornography, which it has banned, the main developer of the software said Monday.

The software, called "Green Dam-Youth Escort," targets online porn by preventing computers from accessing sites with pornographic pictures or language, Zhang Chenmin, general manager of Jinhui Computer System Engineering Co., told The Associated Press.

Jinhui was compiling a database of the blocked sites.

"According to our surveys, many teenage students have become familiar with Internet pornography and they commonly share the addresses of pornographic Web sites with one another," Zhang said.

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The software could also be used to block other kinds of Web sites, depending on keywords, Zhang said.

The Chinese government routinely blocks political sites, especially ones it considers socially destabilizing such as sites that challenge the ruling Communist Party, promote democratic reform or advocate independence for Tibet.

Parents can develop their own lists of sites to be added to the database of blacklisted sites, Zhang said.

"If a father doesn't want his son to be exposed to content related to basketball or drugs, he can block all Web sites related to those things," Zhang said, adding that conversely, users also could unblock Web sites that appear in the database.

Zhang said his company signed a 21 million yuan ($3 million) contract with the Chinese government last May to develop the software and distribute it to personal computer-makers free of charge within one year, to be included with units meant for domestic sale.

Consumers can uninstall the software if they do not want it, Zhang said.

China, which has the world's largest population of Internet users at more than 250 million, this year launched a nationwide crackdown on Internet pornography, which is banned in China.

More than 1,900 Web sites have been shut down since the beginning of the campaign and Web sites including Google and Baidu, China's most popular search engine, were criticized for linking to suspect sites.

According to the Wall Street Journal on Monday, China's Ministry of Industry and Information Technology issued a notice on May 19 to personal computer-makers that PCs to be sold in China as of July 1 must be preloaded with the software.

The program would either be installed on the hard drive or enclosed on a compact disc, the paper reported, adding that PC makers would be required to tell authorities how many PCs they have shipped with the software.

The ministry did not immediately respond to questions from The Associated Press by phone or fax. A separate notice on its Web site said all primary and secondary schools were required to install the Green Dam software on every school computer by the end of last month.

Educators "should fully realize the damage that harmful online information does to the physical and mental health of primary and secondary school students," the notice said.