According to Symantex, W32.Mydoom.M@mm has now been catagorized as a Category 4 virus.

W32.Mydoom.M@mm
W32.Mydoom.M@mm is a mass-mailing worm that drops and executes a backdoor, detected as Backdoor.Zincite.A, that listens on TCP port 1034. The worm uses its own SMTP engine to send itself to email addresses it finds on the infected computer.

The email contains a spoofed From address, and the Subject and Body text will vary. The attachment name will also vary.

For more information and removal instructions, please visit Symantec Security Response: http://securityresponse.symantec.com...doom.m@mm.html

This worm re-emphasizes the basic practice that corporations need to take:
Download and deploy the most up-to-date virus definitions
Turn off and remove unneeded services
Check vendor Web sites for patches and updates
Block or remove email that contains suspect file attachments
Isolate infected machines from the network
Train users not to open attachments unless they are expecting them
Research information about the virus
Trace the path of introduction

Symantec can provide customers support against this worm in several ways:
Symantec AntiVirus solution provide definition file to protect users in multiple levels, including gateway, mail server and client.
Norton AntiVirus prevents infected file to be spread out to other users by using worm-blocking technology.
DeepSight Alert Services and Threat Management System sends a notification when a worm is detected with updates on how to mitigate the risk, information on multiple antivirus vendor updates.
Symantec IDS solutions will have signatures to be able to detect this new worm.