Chen Guangyu is annoyed these days by persistent pop-ups when using MSN Messenger which invite her to click on unfamiliar ads' Web links. They're stubbornly resistent to protective software.

"All my friends deny sending the pop-ups," Chen said. "My ID must be being illegally exploited by spy software."

She is just one of numerous Internet users to have fallen prey to rampant online viruses, trojan horses and spy software that have prompted growing worries about web security in China, whose netizen population, 338 million, is the world's largest.

Li Xiaodong, deputy director of the China Internet Network Information Center (CNNIC), a government-affiliated web research organization, said Saturday China's Web security was in dire need of improved technology and better legal structure to protect net users.

"Hackers' activities are now running wild because they have easy access to free online attack tools," he said.

"Also, a majority of crackers are not aware of the dangers of their pranks."

Hackers, usually computer-savvy geeks who compromise other users' computer security systems to gain unauthorized access, are aware of protective technological benchmarks now becoming much more quickly outdated.

"They can easily obtain free attack tools on hacker websites, and launch assaults like guerrillas. But to defend against them demands comprehensive and powerful security systems," Li said.

Web security in China is far from "developed", said Li. "It's a costly enterprise. We have to try every possibility to close a loophole accidentally found by attackers."

Worse, by plugging trojans into other computers, hackers could easily obtain users' ID, bank numbers and other personal information.

Two 27-year-old men, surnamed Piao and Jin, were arrested on June 16 and June 27 respectively in Yanbian county in Jilin Province on the charge of collaboratively stealing 2.36 million yuan (345,269 U.S. dollars) by breaking into online banking systems, a county police spokesman said Friday.