China faces a serious threat from botnets, networks of computers infected with software that allows them to be controlled remotely for denial-of-service attacks and to send spam, according to a report issued by China's National Computer network Emergency Response technical Team (CNCERT).

During 2007, 3.6 million Chinese computers were infected by software that allowed them to be controlled as part of a botnet, CNCERT said in a report published earlier this month. That report blamed lax computer security as a primary cause of the problem.

The 2007 number represents a big drop over the previous year. Approximately 10 million Chinese computers were bot-controlled in 2006, according to a previous CNCERT report.

CNCERT, which is under China's Ministry of Information Industry, put the total number of bot-controlled computers worldwide during 2007 at 6.2 million.

"That number is much more reasonable than some of the others that have been presented in the past year," said Jimmy Kuo, principal architect at Microsoft's Malware Protection Center, noting the CNCERT estimate means roughly 1 in 200 computers around the world are bot-controlled.

However, the estimate shows Chinese computers are disproportionately affected by the problem, accounting for 58 percent of all bot-controlled computers around the world. Moreover, the CNCERT numbers imply that 4.6 percent -- nearly 1 in 20 -- of the 78 million Chinese computers capable of accessing the Internet and in use at the end of 2007, based on a survey by the China Internet Network Information Center, were bot-controlled.

While bot-controlled computers are an unusually large problem in China, many of these botnets also appeared to be controlled by bots inside the country.

CNCERT found 17,063 bots during 2007, of which 10,399 were located outside China, leaving 6,664 bots that appear to be inside China, although this point was not specifically addressed in the report.

Of the 10,399 bots located outside China, 32 percent of them -- 3,328 bots -- were located in the U.S. The next largest source of bots was Taiwan, which accounted for 13 percent, or 1,352 bots.

(Robert McMillan, in San Francisco, contributed to this report.)