The Chinese Government has launched a six-month campaign against online pornography, rumours and slander as it tries to tighten its grip on the internet.

Chinese web controls are already among the world’s tightest, with internet traffic subject to automatic filters and manual monitoring. The Government encourages web use for education and business but tries to block access to material considered obscene or subversive.

The Ministry of Public Security said the campaign would target cyber strip shows and sexually explicit images, stories and audio and video clips. “The boom of pornographic content on the internet has contaminated cyberspace and perverted China’s young minds,” Zhang Xinfeng, a deputy public security minister, said. He said “content that spreads rumours and is of a slanderous nature” would also be blocked.

China continually upgrades the equipment it uses to control access to the internet, according to OpenNet Initiative, a partnership of British and American Universities that has conducted detailed studies of online censorship in the country.

OpenNet says that China uses a mixture of techniques designed to prevent information reaching the country from the rest of the world, and preventing people within China from talking about forbidden topics. Filters at the gateway to the country's data network block some websites and further filtration is carried out by individual internet service providers.

Within the country, weblogs and chatrooms are kept under close scrutiny. Automated filters prevent posts containing sexually explicit terms or keywords relating to subjects such as the pro-democracy movement and Falun Gong, a religious group banned in China.

Reporters Without Borders, a human rights group, says that China has jailed 50 people for comments they have made on the internet.

Official announcements of the latest internet campaign have focused on pornography. The Xinhua state news agency reported that a third of detainees at the Beijing Reformatory for Juvenile Delinquents were influenced by violent online games or erotic websites when they committed crimes such as robbery and rape.

Online pornography is already illegal, but it remains available to anyone who wants to search hard enough. “The inflow of pornographic materials from abroad and lax domestic controls are to blame for the existing problems in China’s cyberspace,” Mr Zhang said.

Last November, Chen Hui, a website operator, was sentenced to life in prison after being found guilty of running a site containing more than nine million pornographic images.