China's largest mobile operator has assured its subscribers that their user privacy would be protected amid concern over the filtering of text messages for illegal or pornographic content. The country's mobile phone users send out a billion SMSes everyday.

Li Kang, deputy director of customer services for China Mobile, said consumers were not affected by the filter system and said the move is part of wider efforts to clamp down on “unhealthy” mobile web content.

“The freedom and privacy of individual users enjoys legal protection,” China Daily quoted him as saying Friday.

“China Mobile will do its best to protect consumers' rights and interests strictly in line with the relevant laws and regulations.”

His comments were aimed at easing fears over a warning that the company would suspend services to any subscriber found sending illegal content via text message.

The move provoked debate among China's 700 million cell phone users.

Li Mofang, former chief engineer of China Mobile, supported the company's assurance that the filter system does not affect subscribers.

“Only abnormal sending behaviour, such as the distribution of a large number of short massages in a short time, will be the target of monitoring and filtering,” she said.

“The operator has an automatic monitoring system which filters suspicious massages using a set of key words.

“Mobile phone users in China send more than one billion short messages every day. There's no way to monitor all of them,” Li Mofang said.

Many argued that an anti-porn filter system would not work.

Yu Lingyun, a law professor at Tsinghua University in Beijing, told China Daily Friday: “Sexual jokes between friends and couples should not be banned as porn.”

Filtering illegal information is necessary, he said, but a system should also be set up “in case any legal content and communication is incorrectly recognized as porn”.