Experts spotted a new variant of Mydoom virus disguised as an e-mail "sent failed" message, said the Tianjin-based National Computer Virus Emergency Response Center early this week.

The virus, called Worm Mydoom M, attaches to files and then transmits via e-mail to addresses found on the infected machines, according to experts at the center. The virus is disguised as an announcement of an e-mail sending failure.

If the virus gets into a computer, it sets up and modifies certain system files and creates a so-called back-door, a program that sits on your machine to damage files contacted, according to the center, the only anti-virus products testing and certification institution authorized by the Chinese Ministry of Public Security.