Flaws have been found in a controversial internet filtering software that poses a major threat to China's computer security, US scientists have said.

After one day of testing, scientists at the University of Michigan found the Green Dam Youth Escort software contained serious security vulnerabilities that could allow outside parties to take control of computers running it via remote access.

It can also result in private data being stolen and even the shutting down of the computer.

The Green Dam Youth Escort designers said on Monday they were trying to fix security glitches in the programme.

"Yes we are trying to fix it. But this is normal. Any software has bugs," Bryan Zhang, head of Jinhui Computer System Engineering,  told AFP news agency.

China plans to require all computers sold in the country after July to include the web filtering software.

The ministry of industry and information technology issued a notice to computer makers saying the software could either be pre-installed or included with PCs on a separate disc, and that users were not required to use it.

'Computer censorship'
 
Chinese authorities say that the Green Dam Youth Escort software will protect its citizens from pornography.
 
But engineers who have examined the system say it also blocks politically sensitive phrases such as Falun Gong and the 1989 crackdown on pro-democracy protests in Tiananmen Square.

Critics say it is effectively a system for computer-use censorship in China.

Amid the international criticism the move has drawn, it has also received an unusual amount of criticism in Chinese state media.

An online poll conducted last week by Sina.com, a popular Chinese portal, found 81 per cent of respondents felt the move threatened their privacy, while nearly 72 per cent thought it would be ineffective in keeping young people from viewing pornography.

China has the world's largest online population at nearly 300 million internet users.