China's anti-virus authorities on Sunday warned computer users to guard against new mutation of worm virus, which could infect various documents in system.

The virus, Worm_Piloyd.B, could infect documents like exe, html and asp and prevent the system from restoring the affected documents, according to the Tianjin-based National Computer Virus Emergency Response Center.

The virus could force the system to download other viruses from designated websites, according to the center.

Experts suggested computer users update their anti-virus software and use the real-time computer virus monitoring function whenever they surf the Internet.