"The proportion of young people guilty of cheating, rape or robbery who [use] the Internet or have been corrupted by online filth, is very high," spokesman Wu Heping said.
"Our preliminary figures for arrested youth criminals is that almost 80 percent of them have been seduced by the Internet," he said.
Last week China announced a new campaign against Internet pornography, fraud, illegal lotteries and "rumor-spreading," which would protect China's young Internet users from "negative online influences," according to state media sources.
"The public security system will uphold the law during this campaign and also take tips from the public to clean up the pure space of the Internet," Wu said.
Last November the founder of the country's largest pornography website was sentenced to life imprisonment.
Pornography was almost wiped out in China under Mao Zedong, but since economic reforms began and social controls were loosened, it has become more readily available.
China's army of cyber police patrol the Internet for unfavorable content, but they often pay more attention to politically sensitive subjects than pornography or online fraud.