We've published a Virus Alert for the Mydoom Worm:
Why We Are Issuing This Alert
W32/Mydoom@MM spreads through e-mail. This worm can disguise the sender's address, a tactic known as spoofing, and may generate e-mails that appear to have been sent by Microsoft. Many of the addresses Mydoom uses are valid addresses that are being spoofed for malicious purposes.
Technical information about the virus is available from antivirus vendors participating in the Microsoft Virus Information Alliance (VIA). The Mydoom worm is also known by the names Novarg, Shimg, and Mimail.R.
If you ever receive a questionable e-mail message that contains an attachment, do not open the attachment. If you cannot confirm with the sender that the message is valid and that the attachment is safe, delete the message immediately. If you receive a questionable message that purports to be from Microsoft, you should be aware that Microsoft never distributes software through e-mail.
Bottom line... use caution when opening e-mail attachements. Please let your friends and family know about the dangers associated with doing this. Let's keep everybody as safe as we can.