By Michael Bristow
BBC News, Beijing
Every new computer in China will have the software installed
China has defended the use of new screening software that has to be installed on all computers.
Foreign ministry spokesman Qin Gang said the software would filter out pornographic or violent material.
Critics have complained that it could also be used to stop Chinese internet users searching for politically sensitive information.
But Mr Qin, speaking at a regular press briefing, said China promoted the healthy development of the internet.
All computers sold in China - even those that are imported - will have to be pre-installed with the "Green Dam Youth Escort" software.
The news came in a directive from China's Ministry of Industry and Information Technology, and the new regulations will come into force on 1 July.
The directive says the newest version of the software has to be pre-installed on Chinese-made computers before they leave the factory.
Imported computers must contain the software before they are sold.
The aim is to build a healthy and harmonious online environment that does not poison young people's minds, according to the directive.
Mr Qin defended the move on Tuesday: "The purpose of this is to effectively manage harmful material for the public and prevent it from being spread," he said.
"The Chinese government pushes forward the healthy development of the internet. But it lawfully manages the internet," he added.
The Chinese government regularly restricts access to certain internet sites and information it deems sensitive.
The BBC's Chinese language website and video sharing website Youtube are currently inaccessible in Beijing.
Critics fear this new software could be used by the government to enhance its internet censorship system, known as the Great Firewall of China.
But a spokesman for one of the companies that developed the software, Jinhui Computer System Engineering, rejected this accusation.
"It's a sheer commercial activity, having nothing to do with the government," Zhang Chenmin, the company's general manager, told the state-approved Global Times newspaper.