"The most common crimes involve theft, racketeering, fraud of on-line resources and services, mass disruption and inconvenience to the public," said Xu Jianzhuo, deputy director of the Internet security bureau under the Public Security Ministry.

More than 100 million Chinese have Internet access.

Xu said police investigated more than 20,000 complaints of online theft last year, but very few resulted in prosecutions.

He said actual cases of Internet theft from online banks and games accounts alone could be in the millions.

"But just a handful of people have been convicted in recent years," said Xu, attributing the low prosecution rate to inadequate legislation.

Chinese law only forbids hacking into the classified information networks concerning state affairs, national defense, and high-end technology development and stipulates a maximum penalty of three years' jail.

It also forbids sabotage of computer systems by deleting, changing or adding data, with a maximum penalty of five years' jail.

Li Jingjing, from the ministry's security solutions bureau, said that from 1997 to 2005 police investigated 11,521 alleged Internet crimes, but only 14 cases resulted in convictions for sabotage.

"The legislation is so vague that it is difficult to apply in court," Li said, citing its failure to specifically criminalize hacking or sabotage in areas such as healthcare, finance, and energy.

"Soft penalties only encourage more Internet hackers," Li said. Many online crimes were never reported.

The government has launched a series of campaigns in recent years against Internet porn and online gambling.

Xu said the police had made great progress in these areas, but could do little against Internet theft and fraud.

"Hacker activities are rampant," he said.

Police figures show 80 percent of computer systems were hit by one of last year's 72,836 new viruses.

Xu said most hackers now operate for profit, rather than just showing off as their predecessors did.