"Compared with (Internet security issues in) the US, Japan and the Republic of Korea, it is very serious in China," he said.

Last year, 262,000 IP addresses in China were hit by trojans planted by nearly 165,000 overseas IP addresses.

Related readings: Hackers attack Baidu Baidu sues US company over cyber-attack Google's loss could be Baidu's gain Google grabs more eyeballs in China China says Google 'no exception' to law "Those from the US ranked first, accounting for 16.61 percent," Zhou said.

China had the most zombie program-infected computers in 2008, accounting for 13 percent of the worldwide total, with IP addresses in the US accounting for the highest number of hackers.

Overseas hackers have also become a major force in defacing China's websites.

The US was the source of most web-based attacks in 2008, Zhou said, citing a Symantec report on Internet security threats published last April. Symantec is the world's biggest cyber security company.

The report said that 33 percent of the world's zombie servers were located in the US, more than any other country.