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.