The W32/Mydoom.A@mm virus is using some rather sly techniques to persuade you to open the attachment which will infect your computer. One of my old clients asked me about a message that he received. The message looked like it was a returned message (a bounce) that was refused because it contained the W32/Mydoom.A@mm virus. The virus was also sent along as an attachment. Anti-virus scanners do not return mail with the original virus included. They will eliminate it first.

Newsletter publishers may be at the most risk with this one. One, because their email addresses are probably in thousands of address books (their subscribers) and two, because publishers are always dealing with bounced emails and may actually open up the attachment to determine which email address returned the bounce. Instead of being able to remove the bouncing email address from their list, they're infected. Not a good thing, but further justification for publishers to start delivering their newletters via RSS feeds. This is a real email alternative that shouldn't be discounted.
Since I'm always directing folks to McAfee's website, I thought I'd be fair and provide the link to Symantec for this post:

http://securityresponse.symantec.com/avcenter/venc/data/w32.novarg.a@mm.html