Users will know their systems are infected by the worm.whboy if their executable file icons turn into images of pandas with burning joss sticks. [Photo: pconline.com.cn]

Internet security experts are advising computer owners to upgrade their browsers and be on the alert for what could be one of the most devastating cyber worms ever to attack Chinese-language programs.

Hundreds, perhaps thousands, of computers in Shanghai have been infected along with millions of machines in China, the United States and Europe, according to estimates by security experts.

The cyber bug, called worm.whboy because it originated in Wuhan, China, received the first five-star severity rating ever issued by the Shanghai Information Technology Service Center because it can attack local area networks in government bureaus and companies and damage their programs and databases.

So far, it has infected only Chinese-language Windows-based operating systems on computers that have logged onto infected Websites.

The Shanghai center received more than 20 calls about the worm on Monday from companies and government bureaus. Each caller represented a LAN, which can link hundreds, even thousands, of computers, according to Wang Hao, a center official.

"We rated the worm at the top-level because of its serious potential for widespread damage," Wang said. "The most dangerous computer worms last year were Mydoom and its variations. But they were rated 'four-star' as they mainly targeted individual users."

The new worm can also prevent infected computers from operating antivirus software and any programs using the "exe" suffix.

Users will know their systems are infected if their executable file icons turn into images of pandas with burning joss sticks.

Beijing Jiangmin Science Co, an Internet security firm, called the worm a "virus king."

"Our enterprise emergency hotline rang without interruption today, mainly with calls from Guangdong Province and Shanghai," a Jiangmin official said on Monday.

The official estimated "several million" people may be affected by the worm.

Computers in more than 1,000 firms, mostly multinationals, have been infected already, according to Kingsoft Corp, a Beijing-base anti-virus firm.

Cyber security firms and the National Computer Virus Emergency Response Center said that special downloads to fix infected computers are available on antivirus Websites, including www.jiangmin.com and tool.duba.net.

To protect against the worm, experts advised computer users not to open unknown links. They were also urged to raise the security level of their Internet browsers to at least medium and change their Windows entry passwords.