Acer, Lenovo and Sony have stopped bundling Chinese web filtering software with machines that will be sold in the country.

The companies were among just a handful of PC manufacturers that agreed to distribute the Green Dam Youth Escort software after China softened its order for PC makers to do so.

In another sign of fading enforcement, at least one Chinese high school has removed Green Dam from its computers after the software caused "severe conflicts" with programs used for roll and grading.

China originally ordered PC makers to start bundling Green Dam with all computers sold in the country by July to battle internet pornography, but it postponed the deadline under pressure from foreign PC vendors and the US government.

China then said it would not require mass installation of the program by consumers. But the country still said installation would be required for computers in public schools,iInternet cafes and other public places.

China has said the software, which turned out to filter sensitive political content online in addition to pornography, was meant to protect children.

China-based Lenovo, the world's number four PC maker, is no longer pre-installing the program on PCs, though it will include a copy when requested by a buyer, a company spokeswoman.

Taiwan-based Acer, which was shipping a Green Dam CD-ROM with new machines, stopped the practice for new shipments this month, a spokeswoman said. When asked why, the spokeswoman said China is no longer requiring distribution of the software.

Sony stopped shipping the software about two months ago, following Beijing's delay of its mandate, the company said.

Beijing Number 50 High School began installing Green Dam on its computers in June to comply with a government order, but this month it decided to uninstall the program from its networked PCs to ensure "smooth operation of teaching work", according to posts on the school's official blog that have since been removed.

Critics have raised concerns about Green Dam ranging from user privacy and speech freedom to system stability and intellectual property theft. Solid Oak Software , a US vendor of internet content control software targeted at parents, has said Green Dam copied its programming code.

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See also: Lenovo, Acer, Sony sued over China web filte