Chinese police on Thursday said they had arrested a 21-year-old student for running five pornographic Web sites with 210,000 registered users, amid a nationwide crackdown on online pornography that authorities say is "perverting China's young minds."

The student, only identified as Zhu, was detained in the eastern province of Shandong on April 12, after he was suspected of operating five porn sites, containing almost 170,000 pornographic images and obscene movie clips, the Ministry of Public Security announced.

About 210,000 people had signed up to the porn sites Zhu allegedly operated - "Demon's Island", "Global Beauty Pictures", "Community of Bloom", "Moon Alliance" and "Pretty Vines", the police said.

Police also announced on Thursday that they had closed 1,450 porn Web sites and deleted more than 30,000 obscene messages online since the government launched a nationwide campaign to curb the spread of pornography on the Internet on April 12.

Nearly 30 serious porn cases were cracked, the police said, but did not give more details.

The campaign, expected to last six months, will target illegal online activities such as distributing pornographic materials and organizing cyber strip shows, and purge the Web of sexually-explicit images, stories, and audio and video clips, according to Zhang Xinfeng, vice minister of public security.

China had 137 million Internet users at the end of 2006, with most of being young people. The current massive campaign was launched as the government believes the young people need to be protected from negative online influences.

A report by the Beijing Reformatory for Juvenile Delinquents said 33.5 percent of its detainees were influenced by violent online games or erotic Web sites when they committed crimes such as robbery and rape.